Hole in terrain?

I have created whole Island and put houses on it and everything. But now i decide that i want to give my house a basement :S so is there any whay that i make one small part of terrain like hole, so i can put stair there so my character can go under house inside basement?

 

I have the same problem. The only way I found is to make the terrain higher everywhere else and "dig" a hole for the basement. The problem is, the resolution of the terrain doesn't allow be to do a clean cut, so I have to put something all around my house so it's not too visible that the terrain goes down in the wrong place.

I would also welcome a solution to this. Here's what I get.