The Grottes de Vallorbes are a limestone cave system through which the River Orbe flows, carved over millennia by the water eating through the Jura bedrock. The entrance is set dramatically in a cliff face on the edge of town, with the river emerging into daylight from a low, dark arch. The guided tour follows a lit path through chambers decorated with stalactites, stalagmites, and cascades of flowstone, with the river running alongside through sections of the cave.
The tour lasts about an hour and covers around 600 metres of the cave system. The temperature inside holds steady at around 8°C year-round, so bring an extra layer even in summer. The cave formations here are among the most impressive in Switzerland — the combination of flowing water and sculpted limestone gives it a different character from drier cave systems. There is a small mineral museum at the entrance with a well-presented collection of Swiss crystals and regional geology.