A small 12th-century Romanesque chapel on the wooded island of A Toxa, ten minutes' walk across the road bridge from O Grove. The building itself is plain and rectangular, with a single nave and a small bell-tower — except that every surface of the exterior is covered, top to bottom, in nailed-on scallop shells. The texture is extraordinary up close: millions of overlapping shells, weathered to grey-and-white, completely obscuring the original stone.
The interior is unremarkable (a tiny altar, a few candles, the smell of damp). The exterior is the thing. Combine with a walk around A Toxa Island — the wooded paths, the thermal spa hotel, and the small art galleries make for a pleasant afternoon.