This so-called glacier garden has 32 "potholes" that were worn into the sandstone bed of an Iron Age glacier, during the era when ice covered the surface of Lake Lucerne. Discovered and cleared of their debris in 1872, the holes measure up to 9m (30 ft.) wide, and almost as deep. A museum at the site contains a famous 18th-century relief map of the Alps, prehistoric remains of plant and animal life, and a Swiss homeland museum. A 12-minute film is also shown to visitors.