Jay Y.
Yelp
Nothing defines Florence better than its Duomo, and nothing defines the Duomo better than its signature dome! Built centuries after the cathedral's construction by the genius Brunelleschi, the dome was and remained an architectural marvel even today. Although it's an extremely tough and cluster-phobic climb, the dome is a definitely worth a visit to fully appreciate the scale of this dome and the skyline of Florence.
Because the central altar is roped off from the free section of the cathedral, the way up to the dome is the only way to see under the dome. From there, you can get a close-look at the impressive Vasari's Last Judgment fresco, which was intended to parallel Michelangelo's Sistine Chapel fresco! While Vasari's is nowhere near up to par to Michelangelo's because of his skill and lack of funding after, the colorful Last Judgment under the Duomo dome is still a sight to behold.
After climbing more than 400 steps for perhaps 5-10 minutes (Depending on how slow people in front are), you will get a stunning view of Florence. Really, take a break and admire the view; you deserve it! You may be complaining about the climb on the way up, but I bet you will think it's worth it when you see from the tip of the dome.
Now here's the hard part...While I recommend climbing this dome, I don't think it's for everyone especially if you are:
1) Physically unfit (Heart problem, etc. because you'll have to climb back down)
2) Clusterphobic (This is not the place to test that)
3) Short on time*
*I added "short on time" because the line is ridiculously long without the Firenze Card. No matter what time I swing by in the day, the line to the dome is always long. The only way you can skip is the priority line reserved for Firenze Card holder. Florence has many things to see, and spending too much time waiting for one thing is a shame - if you want to see the Florence skyline, the Campanile and Palazzo Vecchio's tower has little to no wait and you are missing out only the dome fresco by choosing these alternatives.
In short, I think climbing the dome is the complete experience to visit and appreciate the Florence Duomo! Vasari's Last Judgment and the skyline view make the climb worthwhile, but the wait will be ridiculous if you do not have the time or a Firenze Card.
Also, don't forget to get the ticket from the office at the Duomo's northwestern corner even if you have the Firenze Card. It would be bad if you lasted through the wait for nothing.
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tl;dr version:
1) See Vasari's dome fresco and the stunning Florence skyline!
2) Tough, clusterphobic climb that is not meant for everyone but worthwhile if you are able
3) Ridiculously long line no matter what time that can be avoided only with Firenze Card