Why Does the Building at Congress and Atlantic in Boston Have No Doors?

[Greg Bernhardt]

I was in Boston this past weekend and noticed this building. It has no doors. It is located directly above the "big dig" and has security cameras lined around the outside. Any ideas what it houses? It's on the Congress and Atlantic intersection.

 

[turbo]

I was in Boston this past weekend and noticed this building. It has no doors. It is located directly above the "big dig" and has security cameras lined around the outside. Any ideas what it houses? It's on the Congress and Atlantic intersection.

Ventilation for the tunnel?

 

[Jimmy Snyder]

Vent?
http://www.flickr.com/photos/rnolan1087/2752098434/"

Edit: scooped.

 

[Andy Resnick]

It's where the aliens are kept.