Nargothrond was a Noldor elves' cave kingdom in Beleriand, ruled by king Orodreth of the House of Finarfin during the First Age. After the disastrous Battle of Unnumbered Tears it remained safe and secluded from any attack until the Noldor elves, led by Túrin Turambar, abandoned secrecy and fought in open battle against Morgoth's armies, which turned out to be catastrophic and revealed their realm's location. This is part of an ongoing project in which I imagine some concepts for a fictitious film based on The Children of Húrin, the book written by John Ronald Reuel Tolkien but edited and finished by his son Christopher.
Banners' design by Gianluca Meluzzi:
https://www.deviantart.com/hurin63/gallery
Check out the Noldor's fortress war engines' design:
https://www.artstation.com/artwork/gRV9EP
Work progress, keyframe 1