Mabul Island, famous for its muck diving, is a small, sand-lined speck of land surrounded by world-class diving in the clear Celebes Sea. Here, Bajau-inspired rows of stilted cottages sit over the water, making up the Sipadan Water Village. The sea is warm and clear, the views are impeccable, the cuisine both western and Asian. As well as all the diving equipment one could need, there is also a bar, a spa, and efficient service from friendly staff.
The Kota Kinabalu fish market is a real eye opener and you can buy some serious tuna steaks.