Duomo - Cattedrale di Santa Maria del Fiore

Truly the most beautiful building I've ever seen. Its majesty almost brought me to tears. I came to Florence on two separate occasions and it was impressive both times. I didn't even need to go inside (though I hear inside is beautiful as well). The amount of detail and beauty was enough for me.

You can buy combined tickets on the spot to most of the attractions, but expect the climb to the Dome to be sold out. A timeslot for that needs to be reserved in advance. However, I enjoyed the view from the tower just the same (the difference between the tower's and dome's heights is somewhere around 50 steps, so no big deal!).

Also important to note that the Cathedral itself is closed on Sundays, I wasn't aware of this. But if you buy the combined ticket that also includes the visit to the crypt underneath the cathedral, the entrance is through the cathedral so you'll still get a glimpse of it from the inside, even if you are not allowed to walk around and explore.

I don't like tour groups at all, but this is one of the few things I highly recommend joining a tour group for this. You DEFINITELY need to schedule in advance, or you'll be waiting for hours. If you don't have skip the line or a tour group, you'll probably still be waiting.

A tour is one of the best ways to guarantee you'll get into the dome, which is absolutely worth it. The dome is a genuine masterpiece. The tower is a separate thing, and you'll have to climb that to really get the best views of the outside of the dome.

Incredible experience. The stairs will wear you out but it's worth it. Definitely get tickets or a tour guide in advance so you don't have as long of a wait.