Basically, your house is built on a concrete raft. (Probably)
To prevent damp entering the house, concrete is poured, a large polythene layer is added, and more concrete- think of it like a pond liner in reverse
If you dig below a couple of inches, there may be pipes/ insulation and eventually the barrier that prevents moisture coming into the living room. You would need to line the pit- or end up with a possible pond
It's not impossible, but not cheap