The reason it doesn't have windows it because it's a telephone exchange. These are, almost universally, windowless shacks in the US. The cloak and dagger bits are just because it's in a convenient location for spying.
Telephone exchanges especially big ones are built for resilience and high security
A few years ago I had to do an update to some of our sun servers in CAPITAL (the really big international Exchange in Edinburgh) interesting experience cavernous rooms and quite spooky with all the various clicks and bleeps
