Hard to say. I doubt is the Earth is so homogeneous in that any sq km is the same as any other, since, while the mantle and core are mostly liquids, they are very viscous liquids, so they don’t mix all that well. The problem from the standpoint of answering the OP is that we don’t have the detailed info about what’s down there. So for all intents and purposes, we may as well assume that they are all about the same.
Going the other way, land owners do not own the rights to the air above their land. No one can, for example, forbid airlines from flying over their property. Or charge them for doing so. So there’s no value to anything above the tops of any buildings.
Atmosphere is atmosphere, so I don’t believe one square km of atmosphere is really worth more than any other one square km of atmosphere. Below one mile, I’d say that is also all pretty much the same. Practically speaking, we’re talking about one square km of the earth’s surface and a small distance beneath it.
In that case, I would say Fort Knox because it contains @ six billion dollars worth of gold.
Doesn’t that give us a lot of leverage over them? I mean, if they don’t play nice, we could just keep it. I’d like to just play in there for a while. Stack the gold bars in such a way that they make a throne, or take a nap on a bed of gold!
The Fed is a for-profit corporation owned 100% by the US Government. Which is why the President has the power to appoint members of its board of directors. But that’s pretty much the limit of the control the government has.
Are you a dragon? Smaug may find a bed of gold confortable, but you won’t.
Anyway, each country’s gold is kept in its own subvault. Occasionally, one country pays another with some of their gold and the Fed moves the appropriate amount from one subvault to another. I believe every once in a while, countries will send auditors over to make sure their gold is still there.
The Fed is actually doing all these countries a service. If they kept the gold themselves, they’d have to build a big vault for it and pay for all the security. I’m sure it’s cheaper to have a single vault than dozens of individual vaults.