Fly to Singapore or Bali. Take 2 hour flight to Manado, Northern Sulawesi, then hire a car to drive you 2 hours or so to Tangkoko Preserve. There are cabins to rent both in and outside the park.
I have been to Tangkoko many times over tha past 15 years and each time it is more appealing. At the end of the day, you can take a dip in the crystal clear sea.
I love all tropical rainforests, and this, in Tangkoko, is gentle or rugged, depending on whether you hike up the volcano or not. It supports rare Tarsiers, habituated troops of Sulawesi Macaques, countless hornbills and zillions of other birds.