Pisa, Italy

It took from 1173 to 1274 to build the tower, and it was already leaning
before they finished. There's a fence around the "low" side and a 16 foot
difference top to bottom (lean)! They've stacked a lot of concrete weights
on the "high" side and attached two bands around the tower with four long
cables which disappear over the roof of someones' house! It's built on sand
and clay.