St. Thomas—check. St. John—check. Even St. Croix—check. Looks like you’ve conquered all of the U.S. Virgin Islands. Not so fast. What about Water Island?

Whether it’s because it’s not a saint, because of its small size, or because it was added to the territory later than the other islands, Water Island is the often-forgotten U.S. Virgin Island. The volcanic island sits in Charlotte Amalie Harbor, three-quarters of a mile south of St. Thomas. Like the other three main islands, Water Island was purchased from the Danish, though not until it was needed for its strategic position to protect St. Thomas’ submarine base in 1944. Today, less than 200 people live on the 500-acre island.

You board the ferry at St. Thomas’ Crown Bay Marina for the 10-minute ride across the sailboat-filled harbor to Phillips Landing. The dock serves as the island’s welcome center and post office. The northeastern part of the island, from Carol Point to Sprat Point, is a gated community. You can access the beaches by the water—no beaches are completely private here—but since you’re walking, head south. You can walk everywhere, and it’s nearly impossible to get lost.

Visit Fort Segarra, on the southern tip of the island. World War II ended before the fort was completed, but you can see the gun emplacements, explore the dark underground tunnels, and climb the watchtowers for spectacular views of the turquoise water and the surrounding islands. Wander around the Carolina Point Plantation. There are only ruins now, but free blacks produced cotton and raised livestock—the Europeans found the land undesirable—during the 18th and 19th centuries. And pass freshwater ponds, where pirates used to stop to replenish their water supply. Many believe there is still buried treasure on the island.

Then head to Limestone Bay, a rugged, secluded beach that’s popular with bird watchers. Supermarket Reef sits just offshore. The reef is unusual, since the coral grow toward the island, rather than parallel to it. This creates grooves that look like the aisles of a grocery store. You might see hawksbill sea turtles, goatfish, and remoras while snorkeling here. Having worked up an appetite, return to the western side of the island. Heidi’s Honeymoon Grill sits on Honeymoon Beach. It has picnic tables, thatched umbrellas, the best burgers in the U.S. Virgin Islands, and delicious fish tacos. The palm-lined beach has soft sand, calm water, and iridescent fish. You walk along the edge of the water, watch kids splashing in the small waves, and say hello to passing locals.

It’s almost time for sunset when you reach the other side of the beach. There are loungers in the sand, floating tables in the water, and live music coming from the beach hut. You order a chili-infused tequila cocktail and join the casual party. You feel right at home on Water Island. And you finally understand why no one is in a hurry to publicize this little oasis.