Gua Susu.

Tucked away on the slopes of Mount Rinjani, Gua Susu offers a starkly different experience from the high-altitude trekking of the surrounding national park. Accessed through a narrow, squeeze-in entrance, this lava-formed cave is famous for its natural geothermal warmth. Inside, a hot spring pool heats the air to create a humid, sauna-like chamber, while pale, milk-colored rock formations—which give the cave its name—glow in the dim light. Beyond its distinct geology, Gua Susu holds deep spiritual significance for locals, who use the quiet, steam-filled sanctuary for meditation. Visited alongside neighboring Gua Payung and Gua Manik, it is a surreal, meditative detour that reveals the volcanic and cultural mystique of Rinjani’s rugged landscape.