Leaning Tower of Pisa
The Leaning Tower of Pisa is the campanile (bell tower) belonging to the Cathedral of the Italian city of Pisa, constructed during the 12th to 14th centuries. The tower attracts millions of tourists each year. Despite its architectural beauty it's most famous for the fact that it leans at an angle due to sandy soil under the foundation. The tower's angle was increasing over time and there was a very real threat of the tower toppling completely. A major project was begun in 1989  to restore it to it's 1838 angle of 13.5 ft from the vertical. The tower was secured with massive steel cables while sandy soil was removed from under the foundation and concrete was injected into the resulting space. The tower was closed to the public for 12 years during the restoration. The new foundation is expected to halt further leaning for the next 300 years, perhaps longer.