Danum Valley is in Sabah of Malaysia.
The right place to visit untouched Bornean rainforest at it best — lush, wet, and dark. Unauthorized access to the Danum Valley Conservation Area (DVCA) is forbidden and two checkpoints on the dirt road from Lahad Datu, the town from which trip to Danum Valley starts, enforce the policy effectively.
There are two options to visit Danum Valley: Danum Valley Field Centre (DVFC) is older and caters mostly to researchers who study the Bornean rainforest; and Borneo Rainforest Lodge (BRL), germinated from DVFC to decrease tourists' pressure from the latter. Offices of both organizations are located at Fajar centre block 3 of Lahad Datu town (GPS WGS84: N5.03007 E118.32604), and required to visit as the only way to reach Danum Valey is by authorized minivan arranged there. Reservation should be done in advance by phone/e-mail.
Minivans between DVFC and Lahad Datu office go three days a week (Jan 2017: Monday, Wednesday, Friday, 3:30PM from LD, 8:30AM from DVFC). Tour operators in KK and possibly in other Sabah towns may offer touristic packages, which are the same two options (plus commission and possibly transportation to Lahad Datu), as the only these two organizations (DVFC and BRL) run two different facilities in Danum Valley.
Fees in DVFC are more or less reasonable (transportation RM120 one way/person, ranger RM20/hr, compact camera/DSLR RM5/RM100, nightdrive/sunset-sunrise drive RM140).
DVFC have a system of poorly labeled trails (and a few maps at the center show the routes, but poorly) for 1-7 hr of walking time, access to most of them are permitted only with ranger. Observation tower are closed for maintenance for a indefinite time (Jan 2017), few smaller towers on the trails for animal observation are closed to tourists. There is no canopy walk in DVFC, in contrast to BRL (for must more cheaper but satisfying option of canopy walks see Sepilok's Rainforest Discovery Center ). There are chances to see big mammals (in contrast to many species of invertebrates) on the tracks, but in the clearings around DVFC few of them may be easily spotted (eg. sambar and muntjak deers, bearded pigs, long-tailed macaque, civets, also as monitor lizard and birds).
Lodging in both places are heavily overpriced (Jan 2017: dorm RM96, sheltered plank bed RM78).