Depending on the technology of the attackers the International Space Station would be almost impossible to breach, though you could siege it by attacking it’s supply lines, leading to the crew dieing and the station burning up - or otherwise destroy it, but to breach it in a way to capture it, I can’t see how.
It’s not really the most secure facility “on earth” though… seeing as it’s in, y’know, space. 
Since this is the Straight Dope it wouldn’t be the same without some nitpicking. Fort Knox is no more or less secure than any other army post. In fact prior to 9/11 it was an open post. You could drive right through it. I don’t think there are any open posts any more. I went to basic training there and later Armor Officer Basic. It is the home of the Army Armor Center and of the Army Recruiting Command as well as some other units. (last I heard they were going to move the armor center to Benning along with the crunchies. I don’t know where that stands, I’ve been out of the tank business for a while)
When most people say “Fort Knox” they are actually talking about the United States Bullion Depository which does occupy a small bit of the post. The wiki article makes it seem that the entire armor school is ready to jump to the defense of the depository. I guess they could throw something together if it comes up but most people on post don’t even think about the depository. It’s just a building you drive past sometimes.
ETA the basic training part of Stripes was filmed at Ft Knox. I ran on the same obstacle course 
Yeah, but you’d be watching as a detatched observer. Goldfinger was the only Bond film until Live and Let Die (almost a decade later) that didn’t involve SPECTRE.
I don’t know that you’d call it a “post” since there are no significant number of active duty personnel stationed there, but you can drive right through Fort Hunter Liggett with just a valid ID and proof of car insurance. It’s a beautiful drive, and about the only way through the Santa Lucia mountains.
Stranger
I think the building in question would have to have less human guards and more in the terms of electronic protection if it is to win the title. The more humans that are in close prox to the actual thing being guarded make the thing being guarded more vulnerable, even if the humans are the guards themselves.
Aren’t DNS servers redundant? If you were to clobber one of them wouldn’t the backup just come on line and patch through?
Taking out any single root DNS server wouldn’t do much besides introducing some slight lag on the Internet.
You could generate much more trouble by hacking them and hijacking a few thousand domains…
Site R on Google Maps. And the entrance to the secret underground lair.
Looks susceptible to the ol’ James Bond ski attack if you ask me… 
Edit: oops, just read this on the Wiki page…
Well, the Federal Reserve Bank in NYC has more gold than Fort Knox, so… hopefully it’s at least as secure, if not more?
Re Fort Knox, I’m sure I remember reading somewhere that it’s rumoured to be a decoy, and all the gold is actually kept out back of a Wal-Mart in Idaho, or somewhere. (I’m exaggerating, obviously, but that was the gist.)
It’s pretty secure.
Tours of the NY Fed, including the gold vault, are open to the public, but reservations are required.
The gold vault is located deep underground on NYC bedrock. Those planning a heist should consult the 7.5MB .pdf file located at the first link.
According to the Wiki, there’s a conspiracy theory that Lyndon Johnson moved most (but apparently not all) the gold to London.
What the Americans would have gotten out of doing so is not explained.
It’s actually kept underneath the big fountain at Lenox Square in Atlanta.
Wow, those black helicopters sure got here fast.
And on a re-read of this thread, I’d submit to you that Air Force One, while in flight, is the most secure facility on Earth.
Tripler
And this is despite the Presidency of Harrison Ford.
Am I the only one here who remembers Die Hard 3?
Oddly enough, yes. Yes you are.
That was the whole plot. The bad guys were robbing the Federal Reserve Bank in NYC. The point was made in the film that it contained much more gold than Fort Knox.
Didn’t read all of the thread, but:
Area 51 has to be up there.
Also, there is a Facility in Maryland that houses all of the most dangerous germs in the world, up to 5 stages of deadliness. Can’t think of it, though.
My point. Stranger on a Train pointed out how ludicrous the plan was, so I talked Auric Goldfinger into trying it. He was obsessed enough with gold to actually do it, and he had cheated me once at cards, you see.
That’s really impressive, considering that the CDC only specifies four levels of biocontainment.
I think you’re talking about USAMRIID, though.