Once again, not a cathedral, but I will use it to introduce Italy. It is a small church which looks unassuming, but has phenomenal artwork within.
San Pietro in Vincoli is the traditional holding place of the chains that held Peter in Rome, and has the tomb of pope Julius II. It was originally built in the 5th Century, but has been renovated several times, most notably in the middle ages at the end of the 15th Century by Julius II.
The outside is unassuming....you'd walk right by it if you weren't looking. While I was there, they were preparing it for a wedding.
Inside it has long hall with traditional medieval arches and design:
But the coolest architecture is in the tombs. This is the tomb of Julius II (the same one who commissioned the Sistine Chapel):
It was intended by Julius II to be much larger and have a prominent place in St. Peter's, we all know that the plans of mice and men....
It contains one of my favorite statues, Michelangelo's Moses. In person, the statue looks as if it is about to come to life. The picture doesn't do it justice:
A last cool part is the tomb of Cardinal Cinthio Aldobrandino, since it has a large sculpture of the grim reaper....exactly what you expect to see in a church, right?