Image © Mike Aquino, licensed to About.com.
When visiting the Central Bali town of Ubud, the Sacred Monkey Forest is quite easy to find. If you're at the town center at the junction of the tourist center, the Royal Palace, the Art Market and Warung Ibu Oka, just look for Jalan Monkey Forest and head due south until the road veers to the east. The entrance to the Sacred Monkey Forest is located right on the crook of the road. (8°31'3.597"S, 115°15'33.812"E; location on GeoHack.)
While inside, you are completely at the mercy of the hundreds of macaques living in the Monkey Forest. The monkeys have been spoiled by human contact: the local villagers feed them (believing the monkeys to serve as guardians of the holy structures contained within the forest), and the tourists provide them with supplemental dining and plenty of additional entertainment - make no mistake, you are the subject of their amusement, not the other way around.
The structures they guard, though, are objects of beauty, even for the unbeliever: the large pura dalem, or "temple of death", is a focal point of worship for Padangtegal villagers - a place where they bury and cremate their dead in accordance to Balinese Hindu belief. The chattering monkeys do not detract from the temple's charm; the monkeys swarming over the statuary gives the pura dalem a living authenticity you won't find on any other temple in Bali.
For more on this sacred site in Ubud, read this article: Sacred Monkey Forest.