Item from harry-potter-goblet-of-fire by
A shallow stone basin for viewing extracted memories — Harry falls into it accidentally and witnesses Dumbledore's memories of Death Eater trials, including the sentencing of Barty Crouch Jr.
Harry discovers the Pensieve by accident — Dumbledore left it on his desk, and Harry's curiosity pulled him into a memory before he could stop himself. He falls into a courtroom. He watches Igor Karkaroff — the current Durmstrang headmaster — stand trial and name Death Eaters in exchange for his own freedom. He watches Barty Crouch Jr scream his innocence as his father sentences him to Azkaban. He watches Ludo Bagman's trial, where the former Quidditch player was accused of passing information to Death Eaters and acquitted because the Wizengamot liked him. These memories are Dumbledore's private files — the evidence he's been collecting for years, the patterns he tracks. Harry seeing them is an accident, but not an unproductive one. When Barty Crouch Jr's face emerges from Moody's disguise at the end of the year, Harry recognizes it from the Pensieve. The memories were a warning he couldn't read until it was too late to matter.
A wide, shallow basin of carved stone inscribed with runes. The surface holds a silvery, gaseous substance. Touch the surface and you fall in, landing inside the memory as an invisible observer.
Also known as: the Pensieve, Pensieve, Dumbledore's Pensieve