Angband:

Melkor's stronghold, built after he destroyed the two lamps it was built under the Ered Engryn. Though it was partially destroyed when the Valar captured Melkor, it was not completely cleaned out and Balrogs and others still hid there during his captivity. After he escaped from Valinor, Melkor rebuilt it and it was never again taken until the Great Battle that ended the First Age of the Sun. Angband was, of course, destroyed when the most part of Beleriand sank beneath the ocean.