The largest island in Halong Bay, Cat Ba used to be a backpacker's secret. Secret no more, the island is quickly being developed so the time to see it is now. Half the island is protected parkland and a trip to Cat Ba can be as adventurous as you want it to be: hiking in the UNESCO designated national park, caving or kayaking, or a cultural adventure in its restaurants, fishing areas and markets. One plus for travelers is the free Wi-Fi almost all over the island. Walk up to Cannon Fort, above Cat Ba town, for great views of the area.