Mount Thunder also called Gravin Threndor and Peak of the Fire-Lions is a giant mountain located within the Land.
Deep under the mountain is Kiril Threndor also know as the Heart of Thunder. It is a cave of deep power where Drool Rockworm summons Thomas Covenant to the Land for the first time. Covenant says the caves underneath the mountain smell of burning sulphur over the smell of rotting flesh.
Era of the King and Queen
The mountain talked to Berek Halfhand when he thought all was lost when the King had destroyed the Queen's armies leaving him as the only one to fight him. He wept on the mountain slopes saying all was lost and the mountain asked him to pledge himself to the healing of the land. He agreed and so the mountain sent forth Fire-Lions to destroy the King and his armies.