Koh Rok are two islands - Koh Rok Nai and Koh Rok Nok - about 30 kilometers due south of the Koh Lanta. In the dry season, from around November to May, it's a popular day trip from Koh Lanta. Visitors to the islands, which are part of the Lanta marine park, are greeted with spectacular white sandy beaches and generally clear shallow bays that offer great snorkeling opportunities.
Day trips can be booked at just about any hotel tour desk or travel agency. There are some basic overnight facilities at the ranger station for those that want to rough it.