Jajce's Underground Church, often called the Catacombs, is a carved medieval complex beneath the old town, created as a noble burial church rather than a Roman-style catacomb. Its stone chambers, crosses, and cool underground air give Jajce another layer below the fortress, waterfall, and Ottoman streets above.
The site is compact but atmospheric, and it works best as part of a slow walk through Jajce's historic core. Bring a light layer if you linger underground, and check local ticket arrangements. For a town dense with history, this is one of the most distinctive stops.