RELATED APPLICATIONS 
     The current application claims priority to the U.S. Provisional Application Ser. No. 61/937,512 filed Feb. 8, 2014. 
    
    
     BACKGROUND 
     Technological advancements have made personal ownership of a storm shelter more affordable, and hence more available, to the homeowner. The market for storm shelters has grown significantly; underground storm shelters and safe rooms are much more prevalent in new home construction in recent years. There is a market demand for a concealed underground shelter, be it for safe retreat from a storm and/or for the concealed underground storage of valuables such as guns and ammunitions, other valuables, and survival rations such as food, water, medicines and the like. This demand comes from a steady and recent rise in global societal/political turmoil, unrest, threat of war, coupled with the economic instability of major countries around the world. A result is a group of citizens generally referred to as “preppers,” named for the fact that they are preparing for economic and social unrest of varying predicted degrees. This market demand is satisfied by an underground shelter that, when closed, is advantageously concealed to the view of others above ground. It is to these improvements that the embodiments of the present invention are directed. 
     SUMMARY 
     Some embodiments of this technology contemplate an underground shelter having an open-top enclosure and a base. A linkage assembly selectively moves the base between an opened position and a closed position. A lifting mechanism lifts the base in opposition to a force of gravity on the base in the opened position. A concealment object is supported upon the base to conceal the existence of the underground shelter below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Details of various embodiments of the present invention are described in connection with the accompanying drawings that bear similar reference numerals. 
         FIG. 1  diagrammatically depicts a side view of an underground shelter in the opened position that is constructed in accordance with embodiments of the present invention. 
         FIG. 2  is an enlarged detail of a portion of the shelter of  FIG. 1 . 
         FIG. 3  depicts the shelter of  FIG. 1  but in the closed position. 
         FIG. 4  depicts a partial cross sectional top view of the links nesting in the closed position. 
         FIG. 5  is an isometric depiction of the concealment object being a fire pit. 
         FIG. 6  is an isometric depiction of the concealment object being a condensing unit. 
         FIG. 7  is an isometric depiction of the concealment object being a dog house. 
         FIG. 8  depicts modular forms for constructing an underground open-top concrete enclosure that is sized to support the shroud as depicted in  FIG. 1 . 
         FIG. 9  depicts a top view of the concrete forms in  FIG. 5  joined together for pouring the underground open-top concrete enclosure. 
     
    
    
     DESCRIPTION 
     The presently disclosed technology contemplates an underground shelter having an enclosure with an open top. The shelter also has a lid that is selectively moved to a closed position to close the enclosure. The lid includes an above-ground object not normally associated with an underground shelter, in order to conceal the existence of the underground shelter when the lid is closed. 
     For purposes of this disclosure certain embodiments are described in which the enclosure is constructed of concrete, and preferably of a monolithic concrete pour made possible by the use of a modular form system. That modular form system is included in the disclosure of Applicant&#39;s previously filed provisional application Ser. No. 61/892,201 filed on Oct. 17, 2013 which is assigned to the assignee of this application and which is incorporated herein in its entirety. 
       FIG. 1  diagrammatically depicts a side view of a shelter  100  that is constructed in accordance with illustrative embodiments of the present invention. The shelter  100  depicted in  FIG. 1  is in the opened position, such that a user can enter or leave the shelter via an exposed entry  109 . To construct the enclosure  102 , first an oversize trench is excavated and then concrete forms are placed inside the trench. Concrete can then be poured against the forms. When the concrete is sufficiently cured the forms can be removed, as explained below in more detail, exposing the cured concrete in its formed shape of an open-top enclosure  102 . 
     In these illustrative embodiments the top edge  104  of the open top enclosure  102  is formed below grade  106 . A shroud  108  is attached to a portion of the top edge  104 , such as by the plurality of fasteners  110  embedded in the concrete. The shroud  108  generally forms an accessible entry  109  through which users can readily pass to enter or leave the shelter  100 . The shroud  108  can be constructed of structural components that are formed and/or welded metal components, composite material components, and the like. The height of the shroud  108  can be related to the number of steps that are traversed to reach the top edge  104  of the enclosure  102 . Typically, a stair rise of about 9.5 inches is specified for an ergonomically effective stairway. Here, there are two steps  112 ,  114  supported by the shroud  108  and used to stand partially within the entry  109 . Thus, in these depicted embodiments the shroud  108  is about nineteen inches high. Additional steps  116 ,  118  supported by the enclosure  102  are used to stand partially within the enclosure  102  when either entering or leaving the shelter  100 . 
       FIG. 2  is an enlarged detail of a portion of  FIG. 1 . The entry  109  in these illustrative embodiments is rectangular, having a longitudinal length depicted by “L entry .” That L entry  corresponds to the size of a base  120  having a longitudinal length “L base ” such that in the closed position ( FIG. 3 ) the base  120  sealingly engages against the shroud  108  to close the entry  109 . A seal can be attached to either the base  120  or the shroud  108 , or both. The base  120  is latched in a closed position that compressingly engages the seal to seal the enclosure  102  from exterior moisture, debris, and animal invaders. 
     Returning to  FIG. 1 , each side of the base  120  is supported by two links  122 ,  124  that are connected to the shroud  108  at respective lower ends by pins  126 ,  128 , and that are connected to the base  120  at respective upper ends by pins  130 ,  132 . A lifting mechanism  133  exerts a lifting force to lift the base  120 , and whatever is supported by the base as discussed below, against the force of gravity. In the depicted embodiments the lifting mechanism  133  is a gas shock, although the contemplated embodiments are not so limited. In alternative equivalent embodiments a spring and the like can provide the lifting force. 
     Importantly, the parallel links  122 ,  124  keep the platform  120  substantially level at all times when moving between the opened and closed positions. That permits placing a concealment object  138  on the platform  120  that has items that could be spilled or toppled if not maintained in a level orientation. The fire pit  138   1  discussed below, for example, could spill hot embers or lava rocks if it was not held level at all times. In alternative embodiments where holding the object  138  level is not essential, then other configurations for the links can be used. 
     A lever  134  is presented to the user to grasp and rotate clockwise (push/pull downward) to rotate the link  122 , and in turn the base  120 , in a clockwise direction. The other link  124  passively rotates likewise in the clockwise direction. When the links  122 ,  124  rotate past the vertical position, the force of gravity assists the base  120  (and whatever it supports) in lowering until it ultimately can be latched in the closed position, sealingly engaging against the top end of the shroud  108 . The gas shock  133  in these illustrative embodiments advantageously provides resistance against the downward movement to prevent the base  120  from slamming shut on the shroud  108 .  FIG. 3  is a view similar to  FIG. 1  but depicting after the base  120  has been latched in the closed position. In the closed position the base  120  has a catch (not depicted) that engages a latch  135  to resist the opening force of the lifting mechanism  133 . Preferably, the latch  135  is electronically actuated wirelessly so that a user can remotely actuate the latch  135  while walking toward the shelter. In the event of a transmitter failure a manual override can be provided to acutate the latch  135  if the operator has the appropriate credentials, such as by holding a key fob, to grant the operator access to actuating the latch  135 . 
       FIG. 4  is a cross sectional view depicting how the links  122 ,  124  can be staggered laterally so that they can overlap longitudinally in the closed position. The pin  126  is supported in free rotation within a bearing  136  in the shroud  108 . The lower end of the link  122  and the lever  134  are both rigidly affixed in rotation with the pin  126 . The pins  128 ,  130 ,  132  are likewise coupled by respective bearings  136  permitting free rotation, and the lower end of the link  124  is likewise affixed in rotation with the pin  128 . 
     In these illustrative embodiments the pin  126  can extend to span both opposing sides of the shroud  108  forming the entry  109 . This permits attaching the single lever  134  as depicted, midway between the links  122 , so that a force applied to the lever  134  is equally distributed to each of the links  122 . In equivalent alternative embodiments (not depicted) two levers  134  can be provided, each attached closely to the respective link  122 . 
     Returning to  FIG. 1 , the base  120  supports an above-ground object  138  that is intended to conceal the presence of the underground shelter  100  below. That is, generally, an above ground view of the object  138  in the closed position of the shelter  100  ( FIG. 3 ) would intentionally mislead the unknowing viewer into believing that an underground shelter  100  cannot exist beneath the object  138 . For example, without limitation,  FIG. 5  depicts embodiments that contemplate the object  138  being a gas fire pit  138   1 . The fire pit  138   1  is attached to the top side of the base  120 , such as with fasteners passing through apertures  139  in the base  120 . The lifting mechanism  133  ( FIG. 1 ) is specified according to what lifting force is necessary to lift the combined weight of the fire pit  138   1  and the base  120 . The gas can be supplied via a flexible gas line to accommodate the displacement of the fire pit  138   1  when moved to the opened position. Alternatively, the gas can be supplied by a self-contained container of gas that moves with the fire pit  138   1 . 
       FIG. 6  depicts alternative embodiments that contemplate the object  138  being an outdoor condensing unit  138   2  in an air conditioning system. The condensing unit can be an actual functioning unit or it can be a decoy unit. In either event the power and tubing connections are made with adequate flexible loops to permit the condensing unit  138   2  to move to the opened position.  FIG. 7  depicts yet other alternative embodiments that contemplate the object  138  being an outdoor dog house  138   3 . The skilled artisan readily ascertains from these illustrative embodiments that the object  138 , either real or decoy, is something the viewer would be accustomed to seeing in its environment but effectively concealing the fact that it is attached to the lid of the underground storage shelter  100 . An enumeration of all types of such outdoor objects that can be used to perform that function is not necessary for the skilled artisan to understand the contemplated scope of the present technology. 
     With further reference to the concrete enclosure  102  described in brief above,  FIG. 8  depicts a modular concrete form system that is well suited for use in this technology. An end panel assembly  148  is constructed by joining two panels  150 ,  152  together edge-to-edge. Flanges  154 ,  156  at the mating edges of the panels  150 ,  152  provide protuberant surfaces that are well adapted for connecting together with a clamping mechanism  158 , such as a c-clamp or a vise-grip and the like. A flange  160  extends substantially orthogonal to the panel  152 , and another flange  162  extends substantially orthogonal to the flange  160 . Although not depicted, the panel  150  likewise has two orthogonal flanges extending inwardly and downwardly, respectively. Fastening members  164  can be affixed to yet another flange  166  to matingly align with openings in a flange on the side panel assembly  168 . The side panel assembly  168  and the bottom panel assembly  170  are constructed in like manner.  FIG. 9  is a top view depiction of two opposing end panel assemblies  148  and two opposing side panel assemblies  168  attached to the bottom panel assembly  170 . Note that the top-side orthogonal flanges such as  160 ,  162  abuttingly engage each other to position the panel assemblies  148 ,  168  squarely to the bottom panel assembly  170 . Preferably, the corner flanges are diagonally shaped to provide the mitered corners depicted in  FIG. 9 . The completely assembled forms advantageously permit constructing all four sides and the bottom of the enclosure  102  in a monolithic pour. 
     In the foregoing illustrative embodiments the shelter  100  is installed so that its entry  109  is flush with grade  106 . In some embodiments the grade  106  can be an existing concrete floor, such as the fire pit  138   1  ( FIG. 5 ) installed on concrete patio and the like. In that event it is advantageous to modify the concrete enclosure  102  to provide concrete extensions upward to the grade so that the concrete enclosure  102  can be tied to the existing concrete floor. The existing concrete floor is drilled in multiple places to receive reinforcement rods (such as rebar) before pouring the enclosure  102 , to tie the newly poured concrete enclosure  102  to the existing concrete floor. 
     The various features and alternative details of construction of the apparatuses described herein for the practice of the present invention will readily occur to the skilled artisan in view of the foregoing discussion, and it is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
An apparatus and associated method contemplating an underground shelter having an open-top enclosure and a base. A linkage assembly selectively moves the base between an opened position and a closed position. A lifting mechanism lifts the base in opposition to a force of gravity on the base in the opened position. A concealment object is supported upon the base to conceal the existence of the underground shelter below.