The British Virgin Islands comprise around sixty tropical Caribbean islands, ranging in size from the largest, Tortola 20 km (12 mi) long and 5 km (3 mi) wide, to tiny uninhabited islets. The capital, Road Town, is situated on Tortola. They are located in the Virgin Islands archipelago, a few miles east of the US Virgin Islands. The North Atlantic Ocean lies to the north of the islands, and the Caribbean Sea lies to the south. Most of the islands are volcanic in origin and have a hilly, rugged terrain. Anegada is geologically distinct from the rest of the group and is a flat island composed of limestone and coral.