The cave church of San Michele delle Grotte is carved directly into the cliff face of the ravine below the old town. The space consists of interconnected natural cavities expanded and shaped over centuries of use, with faded Byzantine frescoes covering the walls and the ceiling of the main nave. The church was in active use from at least the 8th century — the frescoes date to the 11th and 12th — and it feels genuinely ancient in a way that restored monuments rarely do.
Access is from a path that descends into the ravine from the old town. The interior is dim and the path can be slippery when wet. Admission is charged and opening hours are limited; check locally before making it a special journey.