The gate was an entrance to a tunnel that went beneath the western coastal mountain range of Dor-lómin, which was formed by a rushing "turbulent water". Here was an underground waterfall with a stairway next to it. This tunnel terminated at the Cirith Ninniach, or "Rainbow Cleft", where the water source met the Firth of Drengist.
It was constructed early in the First Age by the people of Turgon, long before Tuor was born. After he moved to Gondolin, the Gate was lost until it was rediscovered and used by Tuor in his escape from the lands of Hithlum.