St. Jakobskirche is Rothenburg's essential church, a Gothic landmark that anchors the town's medieval self-image. The main reason to go inside is Tilman Riemenschneider's Holy Blood altarpiece, one of the great woodcarvings associated with the town.
Rothenburg can feel stage-managed when the tour groups arrive, but the church has real depth. Give it time, look at the glass and side chapels, and use it as a pause from the postcard lanes outside.