St. Joseph's Catholic Church, better known around Ambarawa as Gereja Jago, is one of the town's most recognisable old churches. Its red-brick massing and high central tower give it a different character from the colonial railway buildings nearby, and the church still anchors a small Catholic community in the centre of town.
Come for a short look rather than a long museum visit. It pairs well with the Ambarawa Train Museum and Fort Willem I, especially if you are tracing the town's Dutch-era institutions and the way they still sit inside everyday Ambarawa.