Michel Schreck
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An interesting excursion, worth a visit if you're in the area. The walk up to the entrace of the cave offers some scenic views over the Thunersee (Lake Thun).
The visit and walk through the cave takes around 1 - 1.5 hours. There's also a museum and a small shop selling refreshments and gifts. For those who are very hungry, the restaurant at the exit of the cave will help. We didn't eat there but portions look generous (prices are "generous", too - but hey, it's Switzerland).
Although we visited on a weekend, it wasn't too busy. Considering that it's not far from Interlaken, this was a welcome surprise, making it a more enjoable experience.