The great cavern system in the White Mountains, beneath Helms Deep and the Hornburg. Also known as Aglarond.

The caverns themselves were of ancient origin and believed to have been delved in the Second Age of the Sun by the Númenóreans.

When Gimli first saw them during the War of the Ring, he was amazed at how beautiful they were. He later returned when the war was over, bringing some of his kin from Erebor to colonize the caves. Gimli was then given the title Lord of the Glittering Caves.