License: Creative Commons - Attribution Author: Mike McBey
This of course is a well known place. From some pictures, which concentrate of the tower, it's not obvious that very close nearby is the cathedral.
The tower started to lean soon after construction started, in 1173. It now leans at a little under 4 degrees which doesn't sound much but represents the top being about 3.9 metres (12 ft 10 in) from the vertical.
In my photo the full extent of the lean is not shown as I wanted to include the cathedral as well. The tower is leaning away from me, and to the left.
It's also famous for the scientific experiment which is said to have been carried out by Galileo Galilei when he dropped two objects of different weights at the same time to see which reached the ground first. (They both landed at the same time).