Gondolin is the Elvish city hidden in a valley in J.R.R. Tolkien’s The Silmarillion.
Gondolin is founded by Turgon, a king of the Noldor, in the First Age. Its location is concealed by the Encircling Mountains, and the city is protected from the forces of Morgoth for many years. The name is associated with the Hidden Rock and the city’s secret position in the land of Beleriand.
The city’s secrecy eventually fails through betrayal. Maeglin reveals its location to Morgoth after being captured and tempted with power. Morgoth’s armies then attack Gondolin, and the city is destroyed. Tuor, Idril, and their followers escape, while Turgon dies during the fall.
Gondolin is distinct from Doriath, another hidden Elven realm of the First Age, and from Nargothrond, an underground fortress founded by Finrod. Its destruction is one of the great disasters of the First Age.