Anyone know how to build underground?

[Cubanmm]

The server I currently play on my clan basically owns. We're the largest and have taken down every other clan. Although one group of players claim they have a base under the map with hundreds of rockets and C4 ready for us. My question is, is this done by hacks/Admin Powers/Glitches? And if this cannot be replicated without glitches, would a willing hacker want to help a fellow gamer out and take these kids out? Or at least find me a way down there?

[55dylan]

I could be wrong. But its nearly impossible to build under the map now. They added something so under the map doesnt count as a part of the map basically. So the only way to build under the map at this point of time is being admin. As they can use the /build plugin to do it.