Alqualondë was the 'Haven of Swans', the chief city and haven of the Teleri in Aman. It was known as the 'Haven of Swans' because it was there that the Teleri built their great swan-shaped ships.

Alqualondë was situated in a natural harbour along the north shore of the Bay of Eldamar. The city was built by Olwë and the Telerin elves, and was built of stone, adorned with pearls, and there was a stone arch at the entrance to the harbour. Olwë’s Halls, in particular, were made of pearl and lit with many lamps. In the years of the Trees, it was lit by many lanterns. By the time Fëanor attacked the city, it was walled. It lay to the north of Tirion.

Galadriel, while pondering whether to leave Valinor for Middle-Earth, stayed with her mother's kindred in Alqualondë.

Fëanor, after the Silmarilli were stolen, went to Alqualondë to persuade the Teleri to join in his war against Morgoth. The Teleri were unmoved and would not aid them by lending ships or help them in the building. Fëanor assembled his host to take the ships by force, and many mariners in Alqualondë were killed in the Kin-Slaying.
Encyclopedia entry originally written by Ainulindale