The fictional city hidden in the valley of Tumladen in J.R.R. Tolkien’s mythology is Gondolin. Its name means “Hidden Rock” in Tolkien’s constructed language Sindarin.
Gondolin was founded by Turgon, a king of the Noldor, during the First Age. The city stood in a concealed valley surrounded by the Encircling Mountains of Beleriand. Its location was protected from Morgoth, the first Dark Lord, for many centuries.
The city’s secrecy eventually failed through the betrayal of Maeglin, who revealed its location to Morgoth. Gondolin was attacked and destroyed during the Fall of Gondolin. Tuor, Idril, and their son Eärendil were among the survivors who escaped the ruins.
Gondolin is not the same city as Minas Tirith, which appears in the later history of Middle-earth and is the capital of Gondor during the Third Age. Nargothrond and Doriath are also First Age realms, but they are separate kingdoms with different locations and histories.