Well worth the work out
The cathedral is indeed spectacular from both the inside and the outside, but I think that all people have to climb to the top of the Duomo. It costs 3 euros if I remember correctly, but it was well worth it. after climbing the 500 sum, vertico inducing stairst you reach the top, and I must say that it is well worth the effort. You can see the whole city from atop the Duomo, and it was breath taking.