This is a great place to visit while in Ubud. Go early (they open at 9) and leave before the crowds arrive around 11. The monkeys are at their most active after it rains, so if you're staying in Ubud try to time your visit after a morning rain. Be sure to explore all of the side paths and temples in the sanctuary... this is where some of the best pictures are. Also remember your monkey etiquette: direct stares from you are a threat, so don't; don't get too close to babies, adults are very protective; do not offer them food, you may get bitten or scratched in the melee you create; watch out for the packs of juveniles, they will mob you if you stop or bend down; before you go, learn the difference in appearance between males and females, juveniles and adults.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.