Aragog's Lair

"Craning his neck sideways, he realized that they had reached the ridge of a vast hollow, a hollow that had been cleared of trees, so that the stars shone brightly on the worse scene he had ever laid eyes on.... Spiders the size of carthorses, eight-eyed, eight-legged, black, hairy, gigantic. The massive specimen that was carrying Harry made its way down the steep slope towards a misty, domed web in the very centre of the hollow, while its fellows closed in all around it, clicking their pincers excitedly at the sight of its load."

- Description.

Aragog's Lair was a large hollow located deep within the Forbidden Forest. It was the home of Aragog after he was forced to leave Hogwarts Castle, and later housed a large colony of Acromantula, the children of Aragog and his mate Mosag. It had been cleared of trees, presumably by its inhabitants, and a large domed web sat in the hollow's centre.

Early history
As an egg, Aragog was brought to Scotland in the 1940s by a traveler, and soon came into the possession of Rubeus Hagrid. For a time, he was kept hidden in the Hogwarts Basement. However, Tom Riddle, requiring a scapegoat to disguise the fact that he had opened the Chamber of Secrets, framed Aragog as Slytherin's monster, and Aragog was forced to flee into the Forbidden Forest. There, he presumably found this hollow and began work on making it his home. Eventually, Hagrid provided Aragog with his mate Mosag, and the two would being a colony here.

1993
Under the advice of Hagrid, Harry Potter and Ronald Weasley unknowingly travelled towards Aragog's Lair on 24 May, only knowing that they were "following the spiders". When they got near it, they were attacked by Acromantula, who brought the two before Aragog. Out of respect for Hagrid, Aragog related what little he knew about the Chamber of Secrets to Harry and Ron and refrained from personally attacking them, however, he did nothing to prevent his colony from attacking after their conversation was over. Harry and Ron were saved by the timely arrival of the Weasley's old car, who carried them out into a safer part of the forest.

1996
"Hermione was not taking the path they had followed to visit Grawp, but the one he had followed three years ago to the lair of the monster Aragog. Hermione had not been with him on that occasion; he doubted she had any idea what danger lay at the end of it."

- Hermione Granger accidentally heads towards Aragog's Lair.

On 17 June, as part of a ruse to convince Dolores Umbridge that Albus Dumbledore was working on a weapon of some form in the Forbidden Forest, Hermione Granger led her deep into the forest, unknowingly coming within close proximity of Aragog's Lair. However, her plan to get the forest's centaurs to attack Umbridge resolved before they got too close to it.

Appearances

 * Harry Potter and the Chamber of Secrets
 * Harry Potter and the Chamber of Secrets (film)
 * Harry Potter and the Chamber of Secrets (video game)
 * Harry Potter and the Order of the Phoenix
 * LEGO Harry Potter: Years 1-4