Today Toba[1] is huge volcanic lake with a central island, and a sort of washed out station on the later hippy trail, but still physically interesting to explore. For anyone considering a visit to Sumatra, do check out the nearby taxidermy museum in Medan[2]. It's absolutely incredible. And for surfers, don't miss the island of Nias[3], but fly instead of getting the boat in bad weather, which amounts to a moving vomitorium. Southeast Sumatra has a huge area of largely unexcavated stone ruins to rival Angkor [4] from an ancient, regionally significant civilization and sea power, Srivijaya[5].

[1] https://en.wikipedia.org/wiki/Lake_Toba

[2] https://en.wikipedia.org/wiki/Medan

[3] https://en.wikipedia.org/wiki/Nias

[4] https://en.wikipedia.org/wiki/Angkor

[5] https://en.wikipedia.org/wiki/Srivijaya