Pulau Lakei
This small island has a superb white sand beach. The National Parks Department has a small guard house located on the island. Trips to the island can be arranged with your boatman. There are some mysterious rock paintings just a short walk from the beach
A wide range of animal, bird and plant life including the Proboscis monkeys which come to the mangrove swamp to feed early evening. It's close to the lodging area where covered sheds are built, go there around 4PM, take a book and wait till they come. Seeing Proboscis and other species here is a lot easier and more comfortable than going on a safari. You just walk along an elevated wooden pathway, perhaps 10 minutes from where the boats land.
You can also see the seastacks and a lots more.
Nighttime sightseeing hikes are sometimes led by park staff, and are also easier and more comfortable than ones done on a safari.