This small speck of an island, covered in lush vegetation and with clear blue waters, has a sordid 500-year history as a pirate haven that only came to an end during the reunification in 1975. Today the inhabitants make their living from the sea. A paved motorbike trail circles the island; you can hike up to the hill temple and visit the tranquil beach, and if you come with a Vietnamese speaker, you can arrange to go out with the fishers.
Besides the 2000-or-so inhabitants who reside in the four small, scrappy fishing villages, there's an army base on top of the hill, keeping a vigilant eye out for potential invaders from Cambodia. Rumours of pirate treasure have circulated for years, and in 1983 the army promptly expelled from Vietnam a couple of foreign treasure seekers who arrived illegally by boat from Cambodia, equipped with metal detectors.
The best beach on the island is Bai Bac on the northern coast, which also offers some local beach shacks to feast on fresh seafood. A day trip is possible, but there are now several places to stay, including some basic homestays and guesthouses in the 250,000d-to-500,000d range. Boat trips to nearby islands are available for a negotiable 250,000d. Going out on a fishing boat at night, you may see the sparkly shapes of fish shooting through the water, thanks to the phosphorescence phenomenon.
Minh Nga runs boats to Pirate Island (50,000d, one hour) at 8.15am and 1pm from Ha Tien, returning at 8.30am and 2.30pm.
For more on Pirate Island, see the online Vietnam Coracle guide at http://vietnamcoracle.com/pirate-islands-dao-hai-tac-travel-guide.