The cave system is at sea level and the ocean continually washes into the main cavern which has a floor area of about 2 acres (0.81 ha) and a vaulted rock dome about 125 feet (38 m) high.

At the north, a third entrance is about 50 feet (15 m) above the ocean which serves as an elevated observation area where the entire cave system and its wildlife are visible.

Lichens, algae, and mineral stains cover the cavern walls with greens, pinks, purples, buffs, and reds on the rough surfaces, some of which are named Lincoln's Head, the Indian Maiden, and The Goddess of Liberty.

Many birds make their home at or near the Sea Lion Caves such as the pigeon guillemot, Brandt's cormorant, western, herring, and California gulls, tufted puffins, and the occasional hawk or bald eagle.

Sea Lion Caves were discovered in 1880 by a local seaman, Captain William Cox, who entered the grotto through the western channel in a small boat on a calm day.

He reportedly returned to explore the caves a number of times and on one occasion was marooned for several days because of stormy weather and rough ocean.

Despite the difficulty and danger of the construction, the trail and stairs provided safe access for visitors and the Sea Lion Caves opened to the public in August 1932.

However, word of the attraction spread and the number of people visiting the Sea Lion Caves slowly grew until 1942, when virtually all recreational travel halted due to World War II.