Twice a day — morning and afternoon — rangers put out fruit on a wooden platform at the edge of the national park, and orangutans come in from the surrounding forest. Not all of them show up every session, and the number varies, but it's a reliable way to see them at close range without trekking deep into the jungle.
The morning feeding is generally the better session: quieter, better light, and the animals are more active after a night's sleep. Arrive early. Entry is included in your national park ticket.