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 15 Euro. Expect 45 minutes to 2 hours wait, but there is a lot to see while you wait. It is better if you buy tickets online for 17 Euro well in advance at. Warning, the tickets are non-exchangeable, effectively non-refundable, and only good for the Torre, 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.