There is much more than the Leaning Tower in the city and several different walking itineraries are available.

The leaning tower.
The Piazza dei Miracoli or Field of Miracles is to the north of central Pisa. It’s an UNESCO World Heritage site and contains the city’s most famous sights:

Torre Pendente (Leaning Tower),. The structure was originally conceived as the cathedral’s bell tower. Construction began in 1173 and the tower started leaning soon afterwards due to subsidence of the ground underneath its base. A project to keep the tower from leaning more and tipping over finally reached a successful conclusion in 2001, and the tower is again open to those wishing to climb it.

Climbing the tower requires a reservation-based ticket for €18. Tickets can be bought for the tower on the day, for a specific entry time. This could be 45 minutes to 3 hours after the purchase time, but there is a lot to see while you wait. It is better if you buy tickets online for €17 well in advance at.

Warning, the tickets are non-exchangeable, effectively non-refundable, and only good for the tower, so they’re a bit of a risk to purchase in advance. Make the effort to climb, though, and you’ll be rewarded by the view.

Curiosity: the famous Pisa leaning tower is not the only one, due of the marshy land that they are built on, there are other 2 towers in Pisa: the Bell Tower of San Nicola Church, near the banks of Arno and the Bell Tower of San Michele of Scalzi Church.