Trips to the islands from the Kota Kinabalu jetty are cheap and well organized. We picked a boat company at random and have no complaints. All prices are posted, so there's no haggling. I went to Gaya island and did the rainforest trek from the drop off point to Police Beach, which took about 3 hours round trip. Along the way I saw monkeys, birds, lizards, and wild boars. I would highly recommend it. Other islands are more focused on beaches and water sports.
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