Chaotic First-Time Dungeon Visit

What is it that makes a Fantasy world Fantasy?

The existence of magic? Obviously. The presence of heinous monsters? Thats one as well. The ability to manipulate and rule over the natural elements? Yes. Can be.

But among these factors, there was one that a fantasy world cannot disregard. And what was it?

Yes, the existence of Dungeons.

Standard in games. Obligatory in Isekai animes. Canonical in adventure novels. The Dungeon. Hell, if I played MMROPG and there was no dungeon in that game, Id lash-out to the game devs! Imagine playing Kenshin Contact without having the unlocking of the dungeons event. Id cry. Literally. And then I wont go out of my room for three days.