This first post will be improved as mistakes are found and new ideas suggested.
It's just an idea that I hope somebody will pick up. Maybe not totally a map, but a gamemode in itself... The basic idea is a map crammed full of blocks where you have to dig down to get the intel and then bring it up to the tent.
First, the map will be divided in two halfs, one for each team. A team can dig but not build in its own half. And a team can dig and build in the other team's area. This works for the whole level, except when noted otherwise. So you have to dig a tunnel you can climb up later. If the other team ruins your stairs, you'll have to redig it instead of rebuild it.
Now we divide the map in levels. In the first bottom level, in the middle, we have a cave, with the exact length and width of heaven in regular babel games. It has openings to east and west, the cave's walls are indestructible (godblocked), but both teams may dig and build inside it. The internal space of the cave should be 6 blocks high, I think. It's interesting to make a small buildable warzone. The intels are here.
The second and biggest level should go many blocks high, like the high parts in bridge levels. The middle, right above the cave, should be diggable and buildable by both teams. If the map gets so fucked up that no other way up is possible, the teams will have to find a way to share this space. And you'll see how this connects to the third and fourth levels.
The third one is only one block high. It's full of small indestructible, godblocked platforms. Imagine that, when the level has been dug out too much, players would be forced to build bridges between platforms (yes, they will be able to build on the fourth level), so the platforms would have to be, I don't know, 10 or 20 blocks apart. Each tent is on one of these platforms. Maybe one in the far east and one in the west, maybe in opposite corners, I'm not sure.
The fourth level should have no blocks initially, but space for some comfortable building. Both teams will be able to build and dig there. Ooh, or maybe a team can build but not dig on its own side in the fourth level, but free to do anything in the other team's half? That should bring some clumsy solutions!
Oh, how about different areas having different colors, to avoid confusion? (that'l never work completely though, unless the server can control the colors of new blocks made by players)
It's at least interesting, what do you think?