Questionable Behavior

Okay. I was thinking on my way into work this morning about my time in DC thus far. I have been here for over 3 years now! CAN YOU BELIEVE THAT?!?! It has flown by but at the same time feels like it has been forever. I have been living in the same neighborhood for 3 whole years. I have walked the same way to the Metro in the morning for 3 years and the same way home for 3 years. In all these 3 years something has always puzzled me. In my morning, afternoon, evening and eve weekend walking to the metro I have always noticed and wondered the same thing...
Well, let me back up. In my daily walk I pass a building. It's an unmarked building with only two entrances, that I know of. The two entrances are both blocked by security guards. Now, my building has a security guard downstairs where you flash your badge and keep a walkin'. Not this building. This building, in front of the parking garage doors has AT LEAST 4 men and 2 big dogs standing there with their automatic weapons. We're talking BIG GUYS with BIG GUNS (and not in a "that's what she said" kind of way). I HAVE NO IDEA what is in this building that requires a car check with guns and dogs for everyone that enters it. We're just in a quiet little neighborhood... and they are there AROUND THE CLOCK! It's like, who are they keeping in there? The other entrance has only one guard with one gun, but it is in the tunnel of the metro. I'm telling you, it's bizzaro! I have spent 3 years wondering WHAT IS IN THERE?!?! and I have yet to find the answer. I want to ask, but I don't want to get shot! Any ideas?