Lake Toba

Lake Toba is an immense volcanic lake covering an area of 1707 sq km (1,000 sq km bigger than Singapore) with an island in the center. Formed by a gigantic volcanic eruption some 70,000 years ago, it is probably the largest resurgent caldera on Earth. Some studies say it might have been associated with causing previous ice age/climate change and the largest human population bottleneck ever. Genetic estimates suggests that there where only a few thousand individuals that survived the catastrophe. The island in the middle - Pulau Samosir - was joined to the caldera wall by a narrow isthmus, which was cut through to enable boats to pass; a road bridge crosses the cutting. Samosir island is the cultural centre of Batak tribe who are mostly Christians in the modern days.
Most visitors fly to Medan and then travel by land to Parapat, the town by Lake Toba. Parapat is about 4 hours by car from Medan (4-6 hours by public bus). Public Bus fee is 22,000 IDR. A scheduled and shared 7 passenger minivan costs 60,000 IDR and can be arranged by most hotels in Medan (Feb 08). Raja Taxi +62 (0)617 366-555 operates a shared cab service leaving from Medan airport at scheduled times that costs 75,000 IDR per person (Dec 08). Alternatively, you can book the whole taxi, a Toyota Avanza which seats seven, for 450,000 IDR. Parapat is a nice little town with reasonable hotels/guest houses, good food options and so on. However its on the island itself that you get the real feeling of Danau Toba.
here 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.