The Horcrux Cave

• Type: Natural Sea Cave, Horcrux Hiding Place
• Location: A cliff on the coast of Great Britain
• Owner/Residents: None; used by Lord Voldemort to hide a Horcrux
• Key Features: Concealed entrance requiring a blood sacrifice, a vast underground lake populated by Inferi, an enchanted boat, a central island, and a basin filled with the Potion of Despair.

The cave was first discovered by a young Tom Riddle during an outing from Wool's Orphanage. He used his burgeoning magical abilities to terrorize two other orphans, Amy Benson and Dennis Bishop, inside the cave, an event so traumatic that it was never spoken of in detail. Years later, as Lord Voldemort, he remembered the secluded and intimidating location and chose it as the hiding place for one of his most treasured possessions: the Horcrux made from Slytherin's Locket. To protect it, he wove a complex web of powerful Dark Magic:

• The entrance within the cave was sealed by a magical wall that would only open upon receiving a blood sacrifice.
• Beyond the wall lay a massive, dark underground lake. A small, enchanted boat was hidden at the lake's edge, which could only carry one adult wizard at a time (or one adult and at least one non-adult).
• The lake itself was filled with a horde of Inferi—reanimated corpses—that would attack anyone who touched the water.
• In the center of the lake was a small island, upon which rested a stone basin.
• The basin was filled with the Potion of Despair, an emerald green potion that could not be magically removed and had to be drunk. It induced terrible pain, dehydration, and forced the drinker to relive their worst memories.
• The locket Horcrux lay at the bottom of the basin, accessible only after the potion was consumed.

This hiding place was eventually discovered by Regulus Black, who had defected from the Death Eaters. Accompanied by his house-elf, Kreacher, Regulus bypassed the protections. He ordered Kreacher to switch the real locket with a replica and then to leave without him. Regulus drank the Potion of Despair himself and was subsequently dragged to his death by the Inferi after trying to drink water from the lake.

The cave is the setting for a pivotal chapter in Harry Potter and the Half-Blood Prince. Following information gleaned from the memory of Morfin Gaunt and Hokey the house-elf, Albus Dumbledore deduced the cave's location and invited Harry Potter to accompany him on a mission to destroy the Horcrux. Upon arrival, Dumbledore used his own blood to open the sealed entrance. He and Harry crossed the lake in the enchanted boat. On the central island, Dumbledore drank the Potion of Despair, suffering greatly but successfully emptying the basin for Harry to retrieve the locket. The potion left Dumbledore severely weakened and desperately thirsty. When he attempted to conjure water, and then drank from the lake, he woke the Inferi. Harry fought them off with various spells, but was nearly overcome until Dumbledore roused himself and drove the creatures back with a powerful ring of fire. They escaped the cave and Apparated to Hogsmeade, but the ordeal left Dumbledore critically weakened. This state of vulnerability was a direct factor in the events that led to his death atop the Astronomy Tower later that night. In Harry Potter and the Deathly Hallows, the true story of what happened in the cave is revealed when Harry, Ron Weasley, and Hermione Granger learn from Kreacher that the locket they recovered was a fake, and that Regulus Arcturus Black had sacrificed himself to secure the real one.

• The Entrance Fissure: A dark crack in the cliff face, accessible from the sea, leading into the first part of the cave.
• The Blood-Toll Wall: A rock wall within the cave that magically sealed the way to the lake, requiring a payment of blood to pass.
• The Underground Lake: A vast, pitch-black body of water filling the main cavern. It was used to conceal hundreds of Inferi.
• The Central Island: A small island of black rock in the center of the lake, containing the final protection for the Horcrux.
• The Stone Basin: A basin on the island that contained the Potion of Despair and, at its bottom, Slytherin's Locket.

In the film adaptation of Harry Potter and the Half-Blood Prince, the interior of the cave is depicted as being covered in sharp, crystalline structures. This detail is not mentioned in the novel, which describes the cave walls as smooth and wet. The Inferi attack is also more visually dramatic, with a “whirlpool” of bodies dragging Harry beneath the surface. (Harry Potter and the Half-Blood Prince (film))