Hypthetical for engineers/architects

So I'm on Oahu now, and I went to look at a house up in the heights this past weekend. It sat on the side of a mountain on what appears to be solid rock, and I'd say it was a good 25 feet above street level. No garage, but there was an engineering survey done to bore into the rock to make a 2 car garage ($60k). My question is, how far could you go into the rock? Strictly for daydreaming purposes, could you put large garage underneath as long as you reinforce properly, or is the 2-car pushing it? Lots of varibles, but some general help would be great! Thanks!

 

This is the closest pic I could find to explain. http://www.hicentral.com/properties/prop_detail.asp?listnum=2713765&type=mls

Only difference in the house I looked at is that it sits further forward on the lot, so the garage would be fully covered overhead by rock.