The interior of the cave is filled with water, and won't be revealed by entering it like most other locations. To see inside the cave, the player needs to drink worm blood, which can be obtained by killing a Worm or Giant Worm nearby using the egg that can be obtained from the Giant Tree. The night vision effect of the worm blood is temporary, so it's recommended to either bring the egg with you to kill the worm near the cave entrance, or use an empty flask to collect the worm blood after killing it so you can take it where it's needed. Another method by which the player can see in the cave is to wield a wand with the Torch passive. These wands can sometimes be found in the Mines biome.
Once the player can see inside the cave and the water is removed (by drinking or other means), inside the cave two Maximum Health Increase pickups can be found, as well as a full heal pickup much like the one in the Holy Mountain, making this one of the few sources of healing.