Italy has its Leaning Tower of Pisa. Now, one of England's most iconic towers is starting to tip, as well. According to surveys done in 2011, the clock tower at London's Palace of Westminster, which houses Big Ben, is tilting 18 inches (46 cm) off its original level position, and the lean is getting worse every year. Engineers believe that the tower is sinking into the banks of the River Thames, most likely due to years of underground excavation for the construction of the London Underground's Jubilee Line, an underground parking garage, and sewer systems.
Nevertheless, experts aren't particularly worried. They say that the list of 0.26 degrees, which is visible to the naked eye, means it will take 4,000 years for the 315-foot (96 m) tower to be as tilted as the famous Leaning Tower of Pisa. And that tower is still standing, despite leaning 4 degrees, or about 12 feet (3.7 m), off level. The House of Commons was expected to take up the matter in 2015, but repair work won't begin until 2020 at the earliest.
Aside from the structures mentioned above, the 13th century sandstone tower Qutub Minar in Delhi has a tilt of 25 inches to the southwest. It is believed to be leaning even further due to its foundation and rainwater seepage although experts have taken some precautions like cementing the area with lime.
More about London's leaning tower:
My personal favorite: “The leaning tower of Delft”, the Oude Kerk Delf.