Aek Manik is a clear natural spring on the east side of Lake Toba, used for bathing and swimming. The pale sandy bottom gives the water a bright, clean look, and local stories connect it with the bathing place of King Damanik and his family.
It is a simple nature stop rather than a developed spa. Bring what you need for swimming and treat it as a short detour while exploring the Simalungun side of the lake.