Location from harry-potter-chamber-of-secrets by
A vast library guarded by Madam Pince, where Hermione finds the Polyjuice recipe in the Restricted Section and tears out the page about Basilisks that ultimately saves everyone.
The Hogwarts Library is where Hermione solves the mystery. She gets a signed permission slip from Lockhart (who doesn't read what he signs) to access the Restricted Section and finds the Polyjuice recipe in Moste Potente Potions. Later, she researches pipes, Parseltongue, and creatures with killing gazes, and discovers the answer: a Basilisk -- a serpent born from a chicken's egg hatched beneath a toad, whose direct gaze kills and whose reflected gaze petrifies. She tears the page from the book and is found petrified with it clutched in her stone fist, along with a scrawled note: 'Pipes.' Even paralyzed, Hermione Granger delivers the answer.
Thousands of shelves in towering rows, lit by lamps on each table. The Restricted Section is behind a rope at the back. Madam Pince patrols the aisles like a vulture.
Also known as: the Library, Hogwarts Library, the Restricted Section