100+ mods, combining to make a vanilla friendly experience. Basically minecraft but juiced up, with no quests and freestyle gameplay.
Two mods are the main focus, Deeper and Dark and Anitque Atlas.
Deeper and dark (as explained) lets you ignite a portal in the deep dark using the big structure in the middle, adding a cave world structured on the deeper and darker, and content based around it.
Antique Atlas is the main map for the mod, it can be made with a book and quil along with a compass.