Rowena Ravenclaw's Diadem
Rowena Ravenclaw had a Diadem that bestowed wisdom upon the wearer. This diadem was later on found by Voldemort and made into a horcrux. Harry later on found the diadem in the Room of Requirement, which was then destroyed by Crabbe's Fiendfyre. He found the Diadem by talking to the ghost of Ravenclaw's daughter, Helena Ravenclaw, also known as the Grey Lady.