"Right, of course. Dungeons started appearing in the seventies, at the same time the first espers started awakening. Your standard dungeon is going to spawn somewhere in, normally, a city, with a portal to a pocket dimension, magically yoink maybe one or two dozen people from within a few-blocks radius, stash them inside of itself, and contain some monsters and be sort of on-theme in some way with the monster type and the environment of the dungeon. Like, if it looks like a tomb, it's going to have skeletons or something. The themes are suspiciously centered around concepts that are interesting to humans, like there's dragons and dinosaurs but there's not weird animal mashups we don't have a word for or extinct creatures that get less press than dinosaurs. Somewhere in the dungeon there is a core, which is usually going to be a kind of basketball-sized object hidden somewhere central, sometimes guarded by a boss monster but a lot of dungeons also just have lots of equal monsters instead; destroy the core and the dungeon collapses within a few minutes and is never seen again, any people or things inside irretrievable forever. Many dungeons you can evacuate and kill with a non-superpowered SWAT team or army unit or whatever. If the dungeon is not killed then after a few days it'll despawn on its own, people and things inside irretrievable forever, and then the dungeon - matures, comes back bigger and more effective and streamlined."