Apenheul Primate Park is a zoo in Apeldoorn, Netherlands. It specializes in apes and monkeys. It opened in 1971 and was the first zoo in the world where apes and monkeys could walk around freely in the forest and between the visitors. It started with just a few species, now it displays more than 30 different primates, among them bonobo, gorilla and orangutan.[1] In summer 2011, three adult male proboscis monkeys joined the collection from Singapore Zoo to commemorate the zoo's fortieth anniversary. They are the only known living specimens outside Southeast Asia.