While souvenir hunting at downtown Frankfurt, we saw a what looked like a gothic style lovely church. A metal plaque at its entrance indicated that it's the Alte Nikolaikirche (Old Nicholas Church), a Protestant parish church.
We entered the church and spent an interesting time inside admiring the interior architecture, religious artwork, statutes and artefacts. On the outside the building did not look very large and imposing but once inside, I particularly felt that its interior was huge and the ceiling incredibly high.