The Cave

The Horcrux cave was the cave by the sea where Tom Riddle was taken as a child. As Lord Voldemort, he later used the cave to hide Salazar Slytherin's Locket, one of his Horcruxes. The cave was used again when Regulus Black stole the original locket and when Albus Dumbledore and Harry Potter went searching for it as well.

Early History
In his childhood, Tom Riddle was brought to a seaside site near this cave on holiday with his orphanage. He discovered this cave and terrorised two fellow orphans, Amy Benson and Dennis Bishop, there. He most likely magicked their way to the cave scaring the children. They never spoke of the incident.

Horcrux hiding place
Voldemort later decided to use this cave as a location for one of his Horcruxes (Salazar Slytherin's Locket). Upon storing the locket in the cave, Voldemort set up a large number of complex enchantments, designed to keep others out but still allow him access to the Horcrux, should he desire to visit or remove it.


 * He placed a spell on the cave so that it was impossible to Apparate inside it (though ineffective against house-elf magic, as Voldemort underestimated them).


 * A smaller entrance was made: a door which required a blood sacrifice to open. According to Dumbledore, this was due to a common misconception by Voldemort that physical pain would weaken a person entering the chamber.


 * An Inferi-infested lake separated the entrance of the cave from the Horcrux. Any attempt to use a Summoning Charm to get the Horcrux would cause one or more Inferi to leap out of the water to block the spell's effect. If the water is disturbed, the Inferi would emerge and attempt to drag the intruder into the water to drown, where the intruder would become an Inferius upon death. The Inferi are frightened off by warmth and light.


 * The Horcrux was placed on an island in the middle of the lake. To get there, one had to find an invisible boat anchored to the cavern wall. The boat was enchanted so that only one wizard of age could be transported in it. This once again shows Voldemort's habit of underestimating his opponents, because he did not expect any underage wizard would attempt such feats.


 * The Horcrux itself was in a basin filled with a potion that could not be touched, vanished, transfigured, or charmed; the only way to dispose of it was to drink it. Once drunk, though, it caused the drinker to see "terrible things", to experience almost unbearable burning in one's insides, and to be dehydrated. If the drinker still had strength left after consuming the potion, conjured water would vanish on them and they would have to drink from the lake; upon disturbing the water an army of Inferi would rise from the lake and attempt to kill the attacker.

Attacks
Main article:First Skirmish at the Horcrux cave

The first attack was by Regulus Black and Kreacher after Voldemort asked Regulus Black for a house elf. Regulus Black offered Kreacher and he was taken here. Kreacher was forced to drink the potion and Voldemort left leaving him to get killed by the inferi. Regulus dissaperated back as Voldemort didn't remember or realise that House elf's could apperate in and out. Kreacher told Regulus Black what had happened and Regulus started to hate Voldemort. Regulus worked out that Voldemort had made horcruxes and asked Kreacher to take him back. Regulus drank the potion and ran to the lake and got killed by the inferi.

Behind the scenes
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Appearances

 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Half-Blood Prince (video game)
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 1

Caverne (Horcruxe)