I got the patent back in July of 2000. And I quote…

“Herein is contained a system of gameplay within multiplayer games, where-by, Dungeons may be spontaniously generated. The method used to trigger generation in-context, is mining. Within this method, specifically a few points must be made clear. A dungeon is any natural, or humaniod creation which is…dark, wet, and ‘cave-like’”
“Furthermore the method known as “mining” may be initiated both by NPCs (none-player characters)
or Players themselves. For legal reasons ‘mining’ will be defined as ‘the action of moving debris in search of wealth, materials, or the expansion of a already existent cave/dungeon complex’, whereby the actual ability to mine may be defined as a ‘skill’ within game context, or just a performable action.”

Granted, I patented this idea for the sole reason of Huge Gaming companies from snatching it up:)
If your wondering about other of your ideas, check with me first, because you;d be surprised how many I actually own^_^. There all open for use by organizations that are not-for profit, and or organizations whos income total less then $100,000 USD per Fiscal Year, as well as any organization no larger then 15 people per- the actual development team, and the company as a whole.

As for the mine-shaft idea, there’s a little online game called Wurm Online that does just this. It even allows digging holes and moving dirt among other things. Basically, most of the world can be altered physically by the players. The graphics and interface are horrible, but the gameplay elements are very fascinating.