Calacirya

Calacirya is the pass in the Pelóri Mountains north of Mount Taniquetil where Tirion was set on Túna. After the hiding of Valinor this was the lone gap through the mountains of Aman. The Valar would have closed the mountains entirely but, realizing that the Elves, even the Vanyar, needed to be able to breath the outside air, they kept Calacirya open. They also did not want to wholly separate the Vanyar and Noldor from the Teleri on the coast.

Calacirya means "Cleft of Light" in Quenya (from cálë = "light" and cilya = "cleft, gorge").