Placed right in front of the glorious Duomo, the baptistery harkens back to Florence's beginnings--it's rumored to have been the first religious building raised there. You'll find elaborate mosaic work on the ceiling, and the perfect symmetry of the architecture makes for incredible acoustics. Make sure to check out the floor work, as well. It's been well-preserved after hundreds of years. You'll also want to stop and admire the baptistery doors; they're a major part of Florence's art history. Buying a ticket to the Duomo and its museum also gives you access to the baptistery, so make sure you stop by after touring the larger building.