Lairiang River. Lairiang is the longest river in Sulawesi Island running down from Napu, Besoa, Bada and Gimpu valleys ending into Makassar straits in the west. Napu, Sobek (white water rafting team) form America discovered Lariang River is one of the best rivers for rafting. It has the score IVV grade. Most of these trekkers take this area for their trekking and rafting as well. The rumbling of Lairiang river could be heard from a remote distance, nothing you can see except the huge bluish tropical rain forest as far as your eyes can see.