One of the most beautiful cathedrals I have ever seen on the outside. The large spire in particular is amazing with it's stunning gothic architecture.
Museumsufer is Frankfurt's museum mile. It also happens to run along the Main river. It's a gorgeous area to take a walk, and get your art fix. My favorite is the Architecture Museum! (NB: Most museums are closed on Mondays).
Beautiful ..... worth a visit!
If museums are your thing, take your pick of museums (over 30 of them within walking distance) to visit with the Frankfurt Card. Even if you don't prefer museums hopping, the river view is a great place to walk along.
You can climb the 350 stairs up a narrow staircase to get a unique look all over the city. On Sundays and during services you might not be able to get inside, the tower is open from dawn to dusk, though.The cathedral itself is built on an older cathedral's ruins which were built on top of a Roman bath which was built on top of a Celtic village. Sadly most of those areas are currently being secured and renovated so the tower is your best bet for a look over the construction fencing into the old Roman bath.