North Sumatra has very heterogeneous ethnic groups, and thus, cultures.
The people of the eastern coasts, also known as the Malays (Melayu) have markedly different traditions and culture from Batak highlanders who live around Toba Lake and Samosir Island. Further south, the Mandailings and Angkolas, and Nias Island, have yet more flavors of traditions and culture.
Besides them, there are several ethnic groups who live in Medan and other towns of North Sumatra. Its largest groups are Chinese and Indian, who being naturalized Indonesian citizens. Other Indonesian tribes like Acehnese, Minangkabau, Javanese, etc also live in many parts here. Each of the mentioned tribes as well as the ethnic groups has its own dialect, religion, beliefs, traditional customs, etc. Arts and cultures make this region, a paradise for social scientists.
Among the ancient Indonesian cultures, which can be seen at Samosir Island, are the centuries old tombs of Batak Toba kings and a stone-table with its benches, where the Siallagan chiefs formerly held meetings.