A must do visit when in Ubud. We were staying about 200m away from the forest so were also able to see the monkeys on the road whenever we ventured out of our villa and on our roof stealing coconuts. It's 30000Rp for adults and 20000Rp for children below 12 to enter. It does get busy but not so much that it's impossible to get up close to the monkeys should you wish to. Some of them can be a bit aggressive and the children were a little spooked when they were chased by a large monkey but there are people wandering round to keep them in check. They are a bit cheeky and there are warnings at the entrance to remove sunglasses and hats etc before going in.