Halong Bay is a pristine water environment lined with Karst formations of limestone, rising from the glassy, blue sea. There are over 3,000 islands in this UNESCO World Heritage site, located on the Gulf of Tonkin. Reminiscent of Thailand's Krabi area, the best way to see Halong Bay is on an overnight cruise, where you dine and sleep on the boat, enjoying the Karst formations by day, taking time to swim or kayak, and view the extraordinary sunsets on deck by night. Fetching views can be had from the summit of Titov (Titop) Island, a 15 minute walk from the island's beach, on the itinerary of most boat tours. Several spectacular caves are accessible in Halong Bay, several of which are illuminated.