If you’re looking to save a few euros but want to experience what Il Grande Mueso Del Duomo in Florence has to offer then I’m pleased to say that you can visit the interior of the Santa Maria del Fiore Cathedral for free. But if you want the full experience then you’ll need to purchase a ticket from one the ticket booths around the Piazza (or in the crypt of the Cathedral; it’s not as creepy or ominous as it sounds).
The ticket provides admission to Giotto’s bell tower, Brunelleschi’s Dome, the Museo dell’Opera del Duomo, the Baptistery of San Giovanni and Santa Reparata. Some of these, most notably the dome, also require you to reserve a timeslot; so once you’ve purchased your ticket head to one of the electronic booths (which are stupidly difficult to locate, but there is one in the Museo dell’Opera) to reserve your times at no additional cost. For me, the highlight truly is the climb up the dome. Admittedly this won’t be for you if you don’t have a head for heights (or a heart for stairs) but if you do then the views from the interior balcony above the floor of the Cathedral are the first highlight you’ll encounter. But the true ‘pièce de résistance’ is the view across Florence from atop the dome assuming your lungs don’t give up during the climb or vertigo sets in on the steep ascent along narrow corridors.