You can go by tourist bus (minivan 5-7 persons;) from Parapat (Lake Toba) or Berastagi to Bukit Lawang. Tickets can be bought at local tour agencies
If you want to see Orangutans, head to Bukit Lawang in Sumatra. Initially, I thought my place to find them would be Malaysian Borneo. I had many reasons for visiting Borneo, namely becuase I simply hadn’t been before, but also because I wanted to see some amazing wildlife and spend some time in the jungle.