The Foreign Intelligence Surveillance Court, the body that approved the NSA's program of bulk phone-records collection, is perhaps the most secretive court in America. But to do its business, this panel of 11 federal judges must meet someplace. The question is: Where?

If a movie director were drawing this up, he'd probably put the FISC in a protected bunker, or in a house with the blinds drawn and the lights dimmed. The reality is at once both more mysterious and more mundane, as Eric Mill and Lindsay Young discovered recently.

The FISC sits in the E. Barrett Prettyman Courthouse on 3rd Street NW between C Street and Constitution Ave. — or so we think. The building itself is naturally rather nondescript:

Inside, it's not much different. Just floor upon floor of wooden doors with nothing marking them. Except for one door. This door has a biometric scanner and what looks like a rotating dial, the kind you might see on a gym locker, but more sophisticated. Mill explains:

There are actually two other doors with hand scanners — one right next to this one, and one across the hall — but only this door is also augmented with an intercom system and a grey safe dial.
The dial is seemingly featureless, but if you get close up you'll see a small black glass window on the top of the dial, facing up. The dial appears to be disabled during business hours; the glass window was blank, and an employee who entered the door while I was there simply scanned her hand and opened the door.

We can only infer that this room, on the third floor of the courthouse, is where infamous classified legal decisions take place. Not even the other people who work here know for sure. When reached by email, Mill said nobody stopped him during his mission.

"The security guards at the building entrance usually asked me what my business was after I went through the metal detectors, but I just told them I was visiting, or going to the cafeteria (which I also did), and it was fine," Mill told me. "Neither Lindsay nor I did any sketching in front of the door, and Lindsay did all her drawing at home, otherwise it might have attracted more attention."

Asked whether this was the right place, staffers could only joke to Mill and Young that the location of the FISC was the real-world equivalent of the Room of Requirement.

The Room of Requirement, of course, is the secret refuge in Harry Potter that only reveals itself to a user when he or she really, really needs it. When it appears, it provides the user with everything that's needed. In some ways, this comparison is more apt than the staffers realize: The FISC is not only exclusive and inaccessible to ordinary people, but those who do enjoy access to its secrets have managed to secure virtually everything they could want with it.