Leaning Tower of Pisa

Building began in 1173, and within a few years the tower started to tilt as the soft ground beneath it settled. Work stopped and restarted over almost two centuries, with the builders angling the upper storeys to compensate, and the bell chamber was finished in 1372. Engineers closed the tower from 1990 to 2001, eased soil out from under its raised side and brought the lean back to about 4 degrees. It is now monitored and stable.

The climb is the experience: 251 worn marble steps spiral up inside the walls, and you feel the slope shift underfoot as you go round. At the top hang seven bells, one for each note of the scale; the largest, cast in 1655, weighs about 3.5 tonnes. Before you go in, look for Biduino's late-12th-century relief of two ships and a lighthouse on the wall facing the entrance, a reminder that Pisa was once a sea power.