Should Mars have a tunnel system? If so, how should it work?

I'm thinking a tunnel system would be a good addition to the game, and some other people have mentioned tunnels, too. But the question is, how should it work?

I think it should play differently than the above ground part of the game.

One thing I was thinking is that there should be looters that hit every homestead on the map once over the course of a year, and that half of what they steal disappears from the game as they spend it on having a good time, and the other half gets hidden underground in secret lairs. There wouldn't be any way to create money underground like you can above ground with volcanoes/ruins, although you might run into some stuff the looters left there.

Of course, finding money would only be a small part of it. There'd be stuff to pimp out your homestead, other neat-o items, plus things to do besides finding stuff. Also, on the surface there should be stuff to help you explore the tunnels better, and stuff underground that helps on the surface.

If there gets to be enough interesting objects in the game, there can be a trading section to the game, both "open market" and "person to person". I think that would be cool. Maybe you could find photos of Mars or diaries or some music or something. You could collect background midi music (although if you have that then background music should come standard in the game, this should just be bonus tracks).

I'm thinking there could be 1-2 entrances to the underground (found in a crater) in each 50X50 area. You'd need the borer upgrade (maybe 500 MD) to enter the tunnel system. The tunnel system should be twenty levels deep, with 1-2 entrances to each sub-level per 50X50 area as well. That way you'd have to search to find the next sub-level.

There should be something that lets you go back to the entrance of a tunnel very quickly, because with the entrances so spread out it would be tedious/take too many moves to get anywhere in the tunnel system if you have to cover the same ground every day. Maybe there could be a cannon, like in Secret of Mana, at your homestead that shoots you to the entrances you've found, but underground you'd have to get some underground creature/phenomenon to whisk you to the next level.

Maybe levels 19 and 20 could be just for people who've paid money into the game, and they could start a second base there. Maybe anyone who's paid at least $1 into the game for any reason can access it, but to build a second base/do some other cool thing there you'd have to pay $X, or maybe 20,000 MD or something?

Maybe when you buy your underground lair, you also get 11X11 (instead of 10X10 so that your homestead is in the middle) area as your "territory" that you can do special things with. Maybe booby traps, maybe a monument, maybe other stuff. Territories can't overlap, and if a wall or something would take away one of your spaces, you can claim a different square to compensate.

Then you can invite other players to your lair to do stuff, and if they accept and are online during the scheduled event, a screen pops up asking if they want to be teleported to the event. If they click "yes", they show up there (takes no moves), and when they're done they can be teleported back to what they were doing. During the event you wouldn't lose any moves. Of course, the one doing the inviting would have to be there for the "Do you want to teleport?" thing to pop up. You can invite anyone, even non-paying newbs, to the events as they'd only be able to explore your home and territory while they're there.

You'd also be able to pimp out stuff inside your homestead, make your homestead bigger, and other stuff to impress your friends/make it more fun to attend "events". Booby traps wouldn't affect visitors, only people who were actually spending moves to explore.

Another thing is that the moves/map should work differently. Like say 50X50 squares above ground would be 200X200 squares below ground, and since each square is measured 1/4 as big as on the surface each "move" would be worth 4 times as many clicks apiece. There should be walls and rivers and stuff that you have to go around or float across, or build a bridge to get to. And you should be able to draw a map as you go or find map pieces to the tunnel system. With such a big, complicated underground you'd need to know where you're going/have been.

There could be a few portions here and there where you'd have to go down and then back up elsewhere to get to. That would make it more 3-D instead of just a series of 2-D levels.