The Crystal Mines are a location from the 1985 animated series She-Ra: Princess of Power.
She-Ra: Princess of Power
The valuable Crystal Mines are located in the Kingdom of Elfworld on Etheria. The Kingdom is ruled by King Varn, who was once captured by Catra and her Troopers. She took Varn's throne and set him and all of his subjects to work in the mines. Luckily, Varn's son Prince Storm managed to escape and get help from the Great Rebellion in freeing his father and ejecting the Horde from Elfworld.