Florence's cathedral stands tall over the city with its magnificent Renaissance dome designed by Filippo Brunelleschi, with the baptistery right across. The cathedral named in honor of Santa Maria del Fiore is a vast Gothic structure built on the site of the 7th century church of Santa Reparata, the remains of which can be seen in the crypt.
The exterior is covered in a decorative mix of pink, white and green marble. The interior, by contrast, is pretty stark and plain but quite enjoyable on warm summer days since the temperature inside tends to be cooler.
Please note the clock above the entrance on the inside of the church. It was designed in 1443 by Paolo Uccello in accordance with the ora italica, where the 24th hour of the day ended at sunset... and it still works!
https://www.visitflorence.com/florence-churches/duomo.html