My brother emailed and said he has a friend who's taking the train from Rome to Florence for the day. She was looking for suggestions about the best way to spend one day in Florence, where to go, where to eat, etc. Here's what I said:
It's hard to give advice to someone I don't know because I don't know what type of traveller they are, but if it was me I would:
1) take the 10 minute walk from the train station to the Duomo. Here you could: a) go into the cathedral (Santa Maria del Fiore), b) climb to the top of the Dome, c) climb to the top of the Campanile or d) go into the Baptistry (above) --- my choice would be to go into the Baptistry which is just beautiful with bronze doors by Lorenzo Ghiberti (note: you need a ticket for the Baptistry - info on tickets, hours, prices etc. for the Baptistry and the rest of the Duomo complex is here).