Lake Toba (the Indonesian name is 'Danau Toba', as Danau is the Indonesian word for Lake) is the product of the largest volcanic eruption in the last 25 million years. The lake today is a peaceful place where visitors enjoy the slightly cooler temperature (at 900 metres above sea level), and explore the Batak culture.
For the Batak people, sometimes referred to as the Batak Toba, Samosir island in Lake Toba (connected at the west of the island to the rest of Sumatra by a land bridge), is their spiritual home and an important icon of Batak culture and society.
The island is more than 90% Christian, although Christianity is a relatively recently introduction, brought to the Batak in the 19th Century by the German Lutheran missionary, Ludwig Nommensen. The Batak Christianity is highly syncretic in that pre-Christian beliefs and symbology remain strong, and Samosir island's traditional cultural sites, traditional buildings ('rumah adat'), and vast roadside tombs are a part of most tourists' itinerary.
The major point of access to Lake Toba is from the town Parapat on the eastern shore of Lake Toba. This is less than four hours' drive from Medan Kuala Namu airport, or around seven hours from Bukit Lawang. Passenger ferries from Parapat run throughout the day until 7pm, taking around 45 minutes to cross. There is also a car ferry which runs several times a day until 9pm. After this time it is not possible to cross without a very long (five hours) detour to the west of the island, so if arriving in Parapat at night visitors can sleep shoreside at Parapat, albeit that this would only be for one night, as the attractions of Lake Toba are on the other shore.
The tourist centre of Lake Toba essentially begins and ends at the village of Tuktuk, which is directly across from Parapat. Here you will find all the major accommodation choices. During July and August accommodation is busy/booked up with Western tourists, while for a week or so after Ramadan things will be booked up, and the island may be best avoided as there are so many local tourists. Prices may also rise around New Year.
In Tuktuk you can swim in the lake, and walk between the various hotels and restaurants and general relax.
The most popular attractions at Lake Toba are to visit the Stone Chairs at Ambarita, just a few km from Tukutk, which may once have functioned as a tribal court. There are also traditional houses here. At Simanindo, a few km further north, there is a museum with daily dancing. However neither the museum nor the dancing are especially impressive. At Tomok, just south of Tuktuk there are pre-Christian tombs of tribal kings.
When driving around the island, there are many traditional Batak houses directed with mystical symbols such as the gecko, and the singa. Some have weavers making cloth, and there are various places selling souvenirs, though in general none are of particularly high quality.
The Batak are famous throughout Indonesia for their singing voices, and while in Lake Toba you will almost certainly hear singing, perhaps fuelled by tuak (aren sugar palm wine flavoured with special bark), which is widely consumed in the island.
Batak cuisine has some specialities such as arsik, which is lake carp flavoured with a local andaliman (variety of Szechuan pepper), pork in its blood sauce, and Dali ni Horbo (water buffalo cheese). Mostly these are not available at Tuktuk, which caters more to Western tourists, but can be found on the west of the island at Pangururan.
Driving around the island is rewarding itself, as the islands' mountains reveal beautiful panoramas of the lake below, rice paddies, and other attractive scenery.
The town of Balige on the land side, around 1.5 hours south of Parapat is a traditional Batak town with attractive market, and a newly built museum of Batak culture.