If i understand correctly, the only significant aspect of the leaning tower of Pisa is that it leans. I was curious to know when it became popular, because it was likely not always leaning. What were the circumstances that lead to its fame?
The tower began leaning while It was being built, meaning that the floors are not parallel--as it leaned, the builders changed the angle of the floor they were building. It's actually a beautiful tower, and it was built at the same time as the cathedral next to it, which is also beautiful but not so often photographed.
There are a number of other lovely buildings in the square there.
John the Baptist's tomb is in the cathedral next to the tower. Also, I believe Galileo did experiments from the upper levels of the the Leaning Tower of Pisa.