Magical geological phenomena. Tell me yours please!

Sense I believe in give and take, here's mine.

My explanation for magical dungeons.

Dungeons are a staple of the prog fantasy/ litRPG genres. However I often feel like there's not a good in world explanation as to why? The good examples are the exceptions in my experience.

So I decided to do some finaggling. Here's what I came up with by tying them to very foundations of my world's magic.

Mana flows through the world. It's in everything, however the more living things access the mana and the more It's moved the less likely it is to spontaneously generate anything. This leads to weaker mana in places with large populations and a lot of stuff going on.

Following that rule, mana quickly accumulates in abandoned, or remote places until there's enough for spontaneous mana creations, be they monsters, items, or naturally magical resources.

A mine, while operating would have enough mana flow to rarely generate anything. But abandon it and soon monsters, and other magical generation will occur, creating an RPG style dungeon delve experience.

This same effect happens in ancient forests, tall mountains, abandoned desserts, or anywhere where the mana can settle naturally. However its fastest to do so underground where the naturally flows through the earth are interrupted and can accumulate.

Another favorite is the bottomless pit that's a wizards attempt at tunnel to the otherside of the planet. It worked. But he didn't really understand gravity so he died penduluming through the earth's core until he lost momentum.