Mount Sibayak, Stratovolcano in Berastagi, Indonesia.

Mount Sibayak is a stratovolcano rising above Berastagi, its broad, uneven mass covered mostly in dense green vegetation, with bare greyish patches on the upper slopes. The summit is a jagged ridge of several rounded peaks rather than a single point; the highest, Pintau, reaches 2,212 metres. Steam vents and hot springs remain active on and around the mountain.

The volcano experienced its last major eruption in 1881 and has remained geologically active since then. Thermal processes have continuously shaped the landscape, leaving visible marks that tell the story of the mountain's ongoing geological life.

The mountain holds special meaning for the Karo Batak people who live in the region and have traditional connections to this place. Local communities have long recognized the thermal features as part of their natural environment and cultural landscape.

The most-used route starts at Jaranguda village, about 3 km from Berastagi; from the second post the summit is roughly 1 km, taking 30 minutes to an hour. Other official routes begin at Raja Berneh, passing Lau Sidebuk-Debuk hot springs, and at Tongkoh on the Medan–Berastagi road. Sturdy shoes help on the rocky ground, and sulfur smells are strong near the vents.

A gray sulfurous lake sits at the crater's bottom with gas bubbles occasionally rising through its water. White and yellowish sulfur crystals coat the surrounding rocks, creating a stark mineral landscape that looks like nature's own laboratory.