Behold the glory of Khazad-dûm
"Far below Khazad-dûm, there are abysses, spaces and tunnels not known even by the Dwarves, but known by the Balrog. Unknown Beings gnaw the earth and make them, far from the knowledge of any lore."
Khazad-dûm, commonly known as Moria or the Dwarrowdelf, was an underground kingdom beneath the Misty Mountains. It was known for being the ancient realm of the Dwarves of Durin's Folk, and the most famed of all Dwarven realms.