Danau Toba, or Lake Toba, is about 4 hours from Medan by car, and is home to world's largest crater lake and island-within-an-island. The town of Tuk-tuk on the island is popular with European tourists, and magic mushrooms are freely available look for the magic mushroom and laundry service!.
Batak Toba Traditional House is a-must-see attraction while visiting North Sumatra. For tourism, it centered in Samosir island, while there are more in Balige, Porsea, and Tarutung.