The best way to explore Phang Nga Bay is by sea kayak, and the best time is early morning before the longtail boat traffic picks up. The bay's limestone towers are hollow in places: hongs (Thai for rooms) are tidal lagoons hidden inside the karst, accessible only through sea caves at low tide. You paddle through a low tunnel in near-darkness and emerge into a silent, circular lagoon surrounded by cliff walls hundreds of feet high, with no visible exit. The vegetation inside — including mangroves rooted in salt water — has evolved in complete isolation.
Several operators run guided kayak tours from both Phuket and Phang Nga town; the better ones use inflatable sea kayaks that can be paddled in and out of the hongs without guides pulling them on ropes (a lazier method that damages the caves). John Gray's Sea Canoe, operating out of Phuket, pioneered the concept and still runs respected tours. The national park charges an entry fee for most of the bay's islands.