The portals can be found everywhere in the Wild Zone. They are acting like teleporters and are moving you in the underground or to another small island.
Just like the game Diablo, you have to visit the corridors, fight with monsters, use your healing potions and find loots in the form of weapons, spells, or even crypto. Some monsters will be "boss" because they will be stronger.
The labyrinths will be procedurally generated with a software named Dungeon Architect. With the help of this tool we will be able to create a large number of undergrounds to visit, to keep the player busy for weeks or months of crawling!