Berghaus Eisee is a mountain guesthouse and restaurant near the Eisee lake at 1900m, below the Brienzer Rothorn peak.
Open: mid June to late October
Website: www.soerenberg.ch
Their self-service restaurant is usually open daily 8:30 16:30. They have indoor and outdoor seating with view of the surrounding mountains.
You can also stay overnight here in private room or dormitories. It's typical rustic mountain accommodations. You must bring a sleeping bag liner and house shoes. The exception is the double room, which is fitted out with sheets and towels like a hotel room.
How to get here
First ride the Brienz Rothornbahn mountain train or Sörenberg cable car to the Brienzer Rothorn viewpoint.
Then hike or ride the Eisee chairlift down to the lake. It's common for people to hike down and ride back up, but do whatever works for your group.