The climax of an unforgettable trek, the nation's second-highest sacred volcano is revered equally by Muslims and Hindus (pilgrimages in October or November). A foray into tropical forest, descent into a crater, lakeside camping by moonlight, before the final climb to the lunar landscape of ash and stones - the 3,726m-high summit is well worth the effort. The climb (from Senaru) takes 2 to 4 days, with a halt at the caldera, the lake and the summit.