There are hot springs on the western side of the island just across the causeway from Pangururan. The water is hot. Locals usually use their hands to get some water out of the pool, standing in the pool is possible, but you probably won't be able to swim.The fee to enter to the surroundings is Rp 2,000. The pools are free, there's some special foreigner pool for Rp 10,000.
itineraries
Samosir - Many Big Statues as Cemeteries for Batak people ancestors
Samosir, Simanindo - Batak Museum with traditional dance performed twice daily
Samosir, Ambarita - Stone chairs used for judgement and executions
Samosir, Tomok - Good place for locals and foreigner to shop for souvenirs. vegetable and fruits. There's a tomb for you to visit as well.
Just on the other side of Samosir, near Pangururan are hot springs
From Tuk tuk you can see a waterfall up the mountain behind you. It's a great walk with a rewarding fresh swim.