Riffelsee is a small alpine lake at 2,757 metres on the Riffelberg plateau, accessible from Zermatt via the Gornergrat Railway — get off at Rotenboden station and walk five minutes to the shore. On calm mornings the lake produces a perfect reflection of the Matterhorn, which has made it one of the most photographed spots in Switzerland.
The walk from Rotenboden to Riffelalp takes about two hours along the lakeside path and then down through the Riffelalp hamlet, where there is a hotel and restaurant for lunch. This is one of the classic Zermatt summer walks — good views throughout, manageable for any reasonably fit walker, and well signed. In autumn the surrounding meadows turn gold and the lake is at its most mirror-like.