Ever since I’ve played Dungeon Keeper back in the 90’s, I wanted to have my personal cavern system. It’s just so cool. Then, not ten years later, I began playing TESIII: Morrowind. My favorite occupation in the game: exploring Dwemer Ruins. Side note about the Dwemer of The Elder Scrolls: Atheistic elven scientists and craftsmen who live in underground cities, referred to as “dwarves” by the humans; their dwellings have been deserted for millennia after their sudden disappearance due to a magical catastrophe, but their machines and automatons still work like the day they were constructed, fervently defending said ruins from intruders; a very steampunk atmosphere. I digress.
It would have to be in a geologically stable area. No earthquakes allowed! Surface access should always be easy, so there would have to be an over ground structure, which should also take care of ventilation. For security reasons, though, there should at least be an obscured secondary access and ventilation system, which would be mostly inaccessible during the winter time. Water supply usually isn’t an issue in Central and Eastern Europe or anywhere else than the Midwest of the USA, just build a cistern and there’s more than enough. Electricity is just as easy, in this case I would prefer geothermal heating and electrical power – two stones with one bird!
What else? I wouldn’t want to live there alone. I would want to have a family, as a matter of fact, I would dig that dungeon for a community of ten families, or even a hundred. My own underground town. Let’s call it Vault 1 😉