Several different worlds in one place
Rinjani (3726m, Lombok Island) is the ancient power thriving with life.
Its crater lake is huge and neutral, making it suitable for swimming and fishing.
The hike is very intense and involves ascending to the caldera, a strenuous summit assault, a 1000m drop to the lake, a night at the lake, then a full day descent.
Spending 3 full days in exploration of Rinjani is a great idea, and its landscapes are so diverse it's like travelling through several different worlds in one place.