In J.R.R. Tolkien’s fantasy novel The Silmarillion, the great city built by Turgon is Gondolin.
Turgon, a king of the Ñoldorin Elves, establishes Gondolin in a hidden valley surrounded by the Encircling Mountains. Its concealed location is intended to protect the Elves from Morgoth, the first Dark Lord, during the wars of Beleriand in the First Age.
Gondolin becomes one of the greatest Elven realms of Middle-earth. Its secrecy lasts for centuries, but the city is eventually betrayed by Maeglin, allowing Morgoth’s forces to discover and destroy it. Tuor, a Man favored by the Valar, reaches Gondolin and marries Turgon’s daughter, Idril.
Gondolin is distinct from Nargothrond, another important hidden city founded by Finrod, and from Doriath, the woodland realm of Thingol. Its fall is one of the major tragic episodes recounted in The Silmarillion.