Opalana
A city hidden in the annals of history. It has gone by many names over time such as the City of the Dead, the Dragon's Gem, the Mistveiled City, and the All-Mother's Shade.
It sits in the northern region of Geolga, near the base of the mountains on the border between The Dragonlands and the Human Territories. A unique area called the Divine's Glade or Heaven's Pocket. Today, it is simply referred to as the Veiled Pass. It is an area constantly veiled in mist and full of rocky formations making it a veritable maze. Many expedition teams attempted to catalogue the area but were unsuccessful or disappeared. This gave rise to the legend that this was the place where the All-Mother entered our plane of existence and the mist was to protect it from the unworthy. Rumors that a city rested in the center full of riches and a potential paradise for those who earned the All-Mother's favor still persist today.
That is the city of Opalana, also believed to contain a portal to the afterlife. It is said the city is where the spirits released go to enter their final plane of existence. However, at the end of the year, during Ouroboros, spirits are able to make their way back into the world.
After The Great Rebellion, many claims of the city's divine origins were dismissed although it didn't help people find it.
Who discovered it, who built it, and why remains a complete mystery.
Sometimes with world building like this I wonder how Tolkien-like you're going with your stories. By that I mean that the civilization of this world exists so far back in time that it is separated into ages that can be hidden from or lost altogether from subsequent ages. If that is the case, who would have been there at the beginning? Which species or creatures of your world are primordial? Dragons are a strong candidate given their immortality. The craftsmanship of the city is not necessarily a mark of human hands as dragons can create themselves can't they? And wouldn't it be them that would build a city for eternity when they can remain ageless themselves? Or maybe I'm wrong and you really are including another Tolkien feature, that of progenitor spirits (the Ainur in Tolkien and the All-Mother here) who have left markers of their presence in ancient places like this. Anything is possible in a world, while not filled with traditional magic, still full of amazing creatures impossible in ours.
Anything really is possible. Honestly, I don't have a set end goal here, I've just always been fascinated with the mystery of the past and just love the idea of hidden civilizations and lost histories. It makes me wonder about all the things in our histories we haven't discovered or just don't know. And it's fun to see this world continue to expand and grow. I certainly never intended for it to be this big when I started making it! XD