Ka'ula is a small crescent-shaped islet, located about 23 miles (37 km) southwest of the island of Ni'ihau. The small island is uninhabited, and it is believed that no one ever lived here permanently, even though the island was known to the Native Hawaiians who visited it. Two stone structures have been found near the island's summit, which might have been heiaus (ancient temple sites). The highest point of the island is 548 feet (167 m) above sea level and the total land area is 158.2 acres (0.64 km²).
The island is slowly shrinking due to erosion. There is a large cave on the northwestern side of Ka'ula, which is known as Kahalauaola (Shark Cave). The former United States Lighthouse Service built a lighthouse on Ka'ula in 1932, which was in operation until 1947. The U.S. Navy has been using the island as a bombing target since 1952, and unexploded ordnance might still be found on the island. That's why one needs permission from the U.S. Navy to land on Ka'ula. The waters near Ka'ula are visited by fishermen and scuba divers.