A city in the south of Beleriand, according to JRR Tolkien’s book, The Silmarillion. It was a vast underground fortress, well protected and hidden from the eyes of the enemy. It was built to the south of Brethil, home to the Haladin, the second house of the Edain. These people were exceedingly fierce, and served as another buffer between the hordes of Morgoth and Nargothrond.
Ulmo, lord of the water, instructed Finrod Felagund on where to build Nargothrond. Finrod built it with the help of the dwarves, digging it out until the caves were vast enough to contain the biggest settled population of Noldor. Nargothrond was the largest elf-realm of Beleriand, even though the high king over all the Noldor was Fingolfin, Finrod’s uncle. That is, until he pancaked and his son Fingon became King. Finrod set his brothers to neat little prince-ships in various regions of Nargothrond – Angrod and Aegnor in Ard-Galen and Orodreth as warden of Minas Tirith. Ard-Galen fell during the Dagor Bragollach, and Minas Tirith an unfortunate few years later.
The Nargothrondhrim smiths were renowned throughout the land for their skill and craftmanship. Nargothrond was the veritable cultural center of the world at that time. Now, Fëanor and his sons were mighty smiths, but they were always making stupid oaths and running after orcs. No time for smithing.
Túrin, son of Húrin, the despicable fellow (I don’t understand the people who claim he’s a hero. He married his sister!) inadvertantly caused Nargothrond’s downfall. A bridge was built over the Narog and (obviously) a big bridge in the middle of nowhere was a dead-giveaway to Sauron & co that Nargothrond was nearby. The dragon Glaurung led the attack and after everybody was neatly killed or enslaved, took Nargothrond as his lair and gathered all the treasures, some from Valinor, and made them his hoard. Túrin could’ve saved some of the Nargothrondhrim, at the very least Finduilas, daughter of Orodreth, but he was enchanted by the dragon and foolishly trusted in him, believing that everybody was dead.
And then he went on to marry his sister! What a hero, really. Ugh.
So that was the end of Nargothrond.