or enjoy the view; pranksters may hang banners or execute other sorts of mischief. Tunnel hacking Some universities have utility tunnels to carry steam heat and other utilities. Utility tunnels are usually designed for infrequent access for maintenance and the installation of new utilities, so they tend to be small and often cramped. Sometimes, utilities are routed through much larger pedestrian access tunnels (MIT has a number of such tunnels, reducing the need for large networks of steam tunnels; for this reason, there is only one traditional steam tunnel at MIT, built before many buildings were connected). Tunnels range from cold, damp, and muddy to unbearably hot (especially during cold weather). Some are large enough to allow a person to walk freely; others are low-ceilinged, forcing explorers to stoop, bend their knees, or even crawl. Even large tunnels may have points where crisscrossing pipes force an explorer to crawl under or climb over a pipe — a highly dangerous activity, especially when the pipe contains scalding high-pressure steam (and may not be particularly well insulated, or may have weakened over the years since installation). Tunnels also tend to be loud. Background noise may prevent an explorer from hearing another person in the tunnel — who might be a fellow explorer, a police officer, or a homeless person sheltering there. Tunnels may be well lit or pitch-dark, and the same tunnel may have sections of both. Tunnel access points tend to be in locked mechanical rooms where steam pipes and other utilities enter a building, and through manholes. As with roofs, explorers bypass locks to enter mechanical rooms and the connected tunnels. Some adventurers may open manholes from above with crowbars or specialized manhole-opening hooks. Shafting Buildings may have maintenance shafts for passage of pipes and ducts between floors. Climbing these shafts is known as shafting. The practice is similar to buildering, which is done on the outsides of buildings. Regular use of a shaft can wear down insulation and cause other problems. To fix these problems, hackers sometimes take special trips into the shafts to correct any problems with duct tape or other equipment. A dangerous variant of shafting involves entering elevator shafts, either to ride on the top of the elevators, or to explore the shaft itself. This activity is sometimes called elevator surfing. The elevator is first switched to "manual" mode, before boarding or exiting, and back to