The Cathedral of Santa Maria del Fiore in Florence is a massive church with a triple-nave basilica and an astonishing dome that dominates Florence's skyline. Built in the 14th century, it's a mix of Gothic and Renaissance styles, with stunning marble walls, intricate floor mosaics, and beautiful stained-glass windows. Inside, you'll find famous artworks, like Paolo Uccello's clock fresco and Domenico Di Michelino's portrait of Dante Alighieri. Just remember to dress appropriately for a place of worship if you want to check it out!
There are several tickets type to visit the Cathedral, this is the one I recommend: The Brunelleschi Pass. Adult ticket costs €30 and includes the visit to the Cathedral, Giotto's Bell Tower, the Baptistery, Duomo Museum, Santa Reparata and most importantly Brunelleschi's Dome. You don't have to see everything in one day, as it's valid for 3 days from the date selected.
The view from the Dome is absolutely worth it, even though it might be challenging. If you are claustrophobic, probably it's not for you, as it gets really narrow when you are in the Dome.