Monochrome image of Westminister clock tower
The bottom 61 metres (200 ft) of the Clock Tower's
structure consists of brickwork with sand coloured Anston limestone cladding. The
remainder of the tower's height is a framed spire of cast iron. The tower is founded on
a 15-metre (49 ft) square raft, made of 3-metre (9.8 ft) thick concrete, at a depth of
4 metres (13 ft) below ground level. The four clock faces are 55 metres (180 ft) above
ground. The interior volume of the tower is 4,650 cubic metres (164,200 cubic feet).
Despite being one of the world's most famous tourist attractions, the interior of the
tower is not open to overseas visitors, though United Kingdom residents are able to
arrange tours (well in advance) through their Member of Parliament [1]. However, the
tower has no elevator, so those escorted must climb the 334 limestone stairs to the
top.[10]
Because of changes in ground conditions since construction (notably tunnelling for
the Jubilee Line extension), the tower leans slightly to the north-west, by roughly
220 millimetres (8.66 in) at the clock face, giving an inclination of approximately
1/250.[11][12] Due to thermal effects it oscillates annually by a few millimetres east and
west.