Poring Hot Springs is well worth the visit! I came directly after climbing Mt. Kinabalu, and soaking in the hot water did wonders for my sore muscles, not to mention the beautiful nearby river and rainforest surroundings. Very peaceful.
There were two open pools, one warm and the other very hot. There were also "private" bathtubs that you could fill with water of any temperature you like. The tubs are a little rustic-- a broken faucet here and there, and a little dirt in some-- but if you don't mind a little Southeast Asia style, they're very enjoyable. There was also a pool that was great for a cold plunge after the hot springs.