The mountain
Bisoke is one of the five volcanoes inside Volcanoes National Park, sitting on the chain that runs along the Rwanda–DR Congo–Uganda borders. It is not the tallest — Karisimbi beside it is considerably higher — but it holds the largest crater lake in the Virunga chain, a still green disc in the summit bowl at 3,711m.
The climb
Roughly two hours up in good conditions, longer in bad, and it is steep almost the whole way. The path is deep volcanic mud for long stretches; gaiters and proper boots are the difference between a good day and a miserable one, and porters are worth hiring for the pull. The route passes through the same giant lobelia and Hagenia forest as the gorilla treks, with real chances of buffalo sign, duiker and forest birds.
There are shorter walks to lower crater lakes for anyone who cannot manage the full ascent — worth asking about at the briefing if the group is mixed.
Bisoke or Karisimbi?
Bisoke is a day. Karisimbi is two days with a night camped at 3,700m. Unless you specifically want the higher summit and the overnight, Bisoke gives you most of the experience for a fraction of the commitment — and it fits the day after a gorilla trek without needing an extra night in Musanze.
Booking and timing
Booked as a park activity with a guide from the same briefing point at Kinigi as the gorilla treks, with an early start. Dry season footing is significantly better; see best time to visit.