The Glacier Garden is a small geological park on the hill above the Lion Monument, where a series of smooth meltwater potholes carved by a glacier over 20,000 years ago are preserved in the open air. The site also contains a mirror maze, a museum with dioramas of the Ice Age landscape, and a 19th-century relief model of Switzerland that once stood at the Paris World's Fair.
The potholes themselves — 32 of them, the largest nine metres deep — are the main attraction. Formed when the glacier's meltwater funnelled through cracks in the rock and spun boulders in tight circles, they are as smooth and regular as any carved basin. The museum attached to the garden does a good job of explaining the mechanics and the timeline, with displays of fossils found on site including palm leaves from the subtropical period that preceded the Ice Age.