The sea cave is a location in Point Lookout, entered through the wrecked seatub or the well outside the Ark & Dove cathedral. Tribal leader Jackson uses the cave to communicate with a hologram of Professor Calvert.
The cave consists of a series of passages leading to a main chamber, where Jackson communicates with Professor Calvert. The sea cave is inhabited by swamplurks, mirelurk hunters, and swamplurk queens. Additionally, a lone unnamed friendly tribal wanders the cave and will follow the Lone Wanderer around if he spots them. However, the tribal will often be killed by mirelurks before being encountered.
- The sea cave contains the largest amount of pre-War money in one location in Fallout 3 at 39 stacks; 14 are found in a half-sunken rowboat, and 25 are found in and around a chest with a mattress.
- 11 Confederate hats can be found on the floor of the grotto where Jackson is found.
- In the final room, one may occasionally hear splashing of items dropping into the water pool; this is due to the final room being based below the graveyard, and every so often, a skeleton will fall from the roof of the cave.
- After exiting the cave through the ladder a group of ghouls, which includes a glowing one will be encountered nearby.
- When the player first enters the cave there is a friendly NPC marker directly behind them. Using console commands it is possible to clip through the wall and find an invisible NPC named "The Brain."