The Musée de Cluny puts its medieval collection inside a Roman bath hall and the mansion later built on top of it. The route starts in the frigidarium, the cold room, where the Roman vault still stands more than fourteen metres above the floor on walls banded with limestone and brick. This is the oldest intact roofed interior in Paris. Rooms of carved stone, stained glass and ivory follow, and near the end a square room holds the six Lady and the Unicorn tapestries, woven around 1500.
The two buildings are stacked because nobody wanted to pay to clear the older one. When an abbot of Cluny began a residence on this plot, his master builder set the new house against the standing Roman walls rather than knock them down. That is why you walk out of a bath hall and into a late-medieval mansion without ever leaving the site. The collection arrived later and almost by accident: a private collector rented rooms here for his medieval objects, and after he died the state bought the lot and kept it where it stood. The rooms now run in date order, a change made only in the last few years.