One of Italy's signature sights, the Torre Pendente truly lives up to its name, leaning a startling 3.9 degrees off the vertical. The 56m-high tower, officially the Duomo's campanile (bell tower), took almost 200 years to build, but was already listing when it was unveiled in 1372. Over time, the tilt, caused by a layer of weak subsoil, steadily worsened until it was finally halted by a major stabilisation project in the 1990s.
Building began in 1173 under the supervision of architect Bonanno Pisano, but his plans came a cropper almost immediately. Only three of the tower's seven tiers had been built when he was forced to abandon construction after it started leaning. Work resumed in 1272, with artisans and masons attempting to bolster the foundations but failing miserably. They kept going, though, compensating for the lean by gradually building straight up from the lower storeys. But once again work had to be suspended – this time due to war – and construction wasn't completed until the second half of the 14th century.