Canada

Canada has a land border with Denmark! Win trivia night!

So, wildly stupid tangent, but this is how Doom maps works. Sound propagation moves through adjacent sectors to make "nearby" enemies become hostile. Sectors are polygonal regions of a map with one floor, ceiling, and brightness level.

And they don't have to be contiguous. Originally this is so one switch can lower two pillars or whatever, but there's no logical limit.

Doom has no concept of spawning in enemies. Everything you can kill has to be there, from the start. To make monsters zap in when you enter a room or flip a switch, the trigger has to raise a sector so a hidden box full of angry demons can walk over teleporters. Key word: angry. If they're not hostile then they just stand there.

So anywhere the mapper wants enemies ornery before you arrive, they can make a little square in the middle of nowhere, with one half being a sector you're obviously going to fight in, and the other half being the secret room full of shaved gorillas.