away from the palace are finely coursed, but the interior two walls are more crudely finished. The external windows are almost all 18th-century in origin and made from Portland limestone. The jagged remnants of the former palace walls jut out from the sides of the tower. The moat, now dry, stretches away east from the tower, passing by the former landing stage for boats from the Thames, long and made from ashlar stone. The clearances of the post-war era mean that there are now few neighbouring buildings to the tower, and it is much more visible than in previous centuries. The ground floor of the tower is entered from the north, and is made up of two chambers, a larger room , a smaller turret room in the south-east corner, . The windows in the main room are a mixture of early 18th-century designs, combined with a surviving large medieval window embrasure on the eastern side. The main chamber has elaborate stone vaulting, considered by historian Jeremy Ashbee to be "one of the most impressive medieval interiors in London... an architectural masterpiece". The vaulting features 16 carved Reigate Stone bosses, including grotesque heads, birds, flowers and the devil, some designed to form amusing visual illusions. The ground floor is used by English Heritage as a gift shop and cafe. The first floor is reached by a 20th-century spiral staircase, and follows the same two-room design as the first floor. It has a roof of groin-vaulted Portland stone, probably from the 18th century, and the windows are mostly 18th century in origin, with one 20th century reconstruction. The iron door to the larger chamber carries the date of its installation, 1621, and its lock carries the letters "IR", standing for King James I. The neighbouring room is barrel-vaulted in brick, with a recess in the wall that was originally a latrine, and the original 1719 iron-shutters on its north window. The first floor contains an exhibit on the history of the UK Parliament. The spiral staircase to the second floor is original. The floor continues the two-room design, and the roof, largely a post-war replacement with only a few surviving medieval timbers, is intended to resemble the original medieval design. The fireplace and windows are original, as probably is the 14th-century wooden door to the floor. Both the wall between the two rooms, and its stone doorway, were built in the