Chicomoztoc (the Place of 7 caves)
by Marc SaindonCampaign suggestion:
"Planescape Lite": Chicomoztoc (the Place of 7 caves)
A follow up on my post about Mystaran alternatives for Planescape 5e, which I don't trust Wotci to handle well.
In this scenario, the secret of ancient Oltec portal magitek is finally revealed as what was apparently a tomb complex somewhere in the Savage Coast appears to provide a portal to the Lost City of Chicomoztoc (or maybe Xibalba from mayan myth?), which itself is a hub demi-plane which contains a vast number of portals which link locations within Mystara but also has portals to other dimension. In the center of the city is a huge golden statue of an Oltec high priest. While tampering with it to bring the gold back home, the adventurers re-awaken what it appears to be a unique Orichalcum Colossal Golem, who is both sentient and shows magical prowess; this figure takes the role of Sigil's Lady of Pain as 'manager' of the town. The town's master, quickly dubbed 'El Dorado' by the adventurers, is not hostile and allows the newcomers to set up shop, occupying the now empty city, hoping for its own reasons to bring back trade and people to the hub. While it is knowledgeable about the portal techno-magic, its understanding of the world is pre-Rain of Fire, so the destinations often aren't as it remembers them, leading adventurers to some surprises when they get there.
After several years, enough people are in the secret that the re-populated city of Chicomoztoc now houses 5 factions who struggle for influence and dominance over Portal City's affairs; rather than alignment like in Sigil, these factions align themselves with the 5 Spheres. Placeholders names like the Collegium (Time, nerds), the Arsenal (Energy, jocks), the Clique (Thought, mean girls), the Vault (Matter, preps) and the Downward Spiral (Entropy, emo kids) can be used until better names and concepts are figured out.
(pic from: https://media2.westword.com/den/imager/u/magnum/16863317/olmec-chalcatzingo-mexico.jpg?cb=1684353013)