This looks like the right tool for the job.
Massive Ordnance Penetrator (MOP)
Direct Strike Hard Target Weapon / Big BLU
Boeing's Phantom Works is leading the effort to demonstrate the Massive Ordnance Penetrator (MOP). The three-phase technology demonstration builds on design studies that Boeing had conducted for the laboratory. Flight testing is envisaged around 2006. The 6 m [20 feet] long MOP features short-span wings and trellis-type tails. The 13,600 kg [30,000 lb] weapon contains a 2,700 kg [6,000 lb] explosive charge. MOP is designed to go deeper than any nuclear bunker buster and take out 25 percent of the underground and deeply buried targets. It is expected to penetrate as much as 60 meters [200 feet] through 5,000 psi reinforced concrete. It will burrow 8 meters into the ground through 10,000 psi reinforced concrete. Northrop Grumman is working on with Boeing to develop this conventional bunker buster. They are under contract to Air Force Research Laboratory's Munitions Directorate at Eglin Air Force Base, Florida, and Defense Threat Reduction Agency.
http://www.globalsecurity.org/military/systems/munitions/dshtw.htm
Big Bertha shell could punch through what?- 75m [250ft]- of concrete. It was not easy then, and would not be easy now - one needs a supersonic striking speed, i.e. a terminal propulsion booster [doable] plus a good target hit. Good luck trying to hit with those an offset facility, where ventilation shafts, for example, could be 1000 ft to the side of it, and not directly above.
Looks like 2007 is the year....
2006 - scaled penetration and lethality testing
2007 - Conduct Massive Ordnance Penetrator Demonstration
2007 - full-scale performance demonstration against realistic hard and deeply buried targets