The Duomo is arguably Florence’s most important (and busiest) tourist attraction.
There are three parts of the Duomo you can visit; the dome, the bell tower and the cathedral itself. A ticket costs €10 and this allows you to enter both the dome and the bell tower. You can buy a ticket from a few nearby tourist information shops which aren’t very well sign posted at all but the stewards on the doors will point you in the right direction. You cannot buy a ticket on the doors so don’t be the person that spends hours queuing up to get turned away! This isn’t clearly marked either.
The queues for each section of the Duomo are huge no matter what time of day you go. The only time I didn’t see a queue was at around 8:30 am when it had just opened. We decided to just climb the dome given that we didn’t want to spend our time in Florence queuing up. The dome is a higher than the bell tower and you can also get a few glimpses of the inside of the cathedral on your way up.
The last thing they fail to mention is that to reach the top of the dome, you have to climb over 400 steps up a very narrow spiral staircase surrounded by stone walls. It’s pretty clammy in there and very claustrophobic. Very small children and people with heart problems would probably struggle to get to the top, but those that do make it are rewarded with an incredible view over Florence!