Baarle-Nassau is the name of a town, and the municipality that contains it, in the southern Netherlands province of North Brabant. It's not particularly important. It is, indeed, pretty tiny: less than 7000 people live there.
Baarle-Hertog is the name of a town, and the municipality that contains it, in the northern Belgian province of Antwerp. It is, if anything, even less important. It's certainly smaller: less than 3,000 people live in this one.
The only reason any outsiders take notice of either of these places are because of their relationship to each other. This is Baarle-Nassau...
...and this is Baarle-Hertog:
When we suggested that this building, which sits half inside and half outside London's city limits, was the stupidest city boundary in the world, we might in retrospect have been being a tad naive.
This slightly crazy situation in the Baarles dates all the way back to the 12th century, when a series of treaties and commercial deals split the local lands between the lords of Breda and the dukes of Brabant. In the centuries that followed, the two areas would sometimes be part of the same political entity, and sometimes be governed separately.
But somehow, the vague absurdities of the border were never addressed. The border between Belgium and the Netherlands was formalised by the 1843 Treaty of Maastricht; but since that drew the line in such a way as to put Belgian Catholics on one side and Dutch protestants on the other – even if that meant going through the middle of buildings – it didn't do much to simplify things.
The result is that the Belgian town of Baarle-Hertog consists of 26 separate bits of land inside the Dutch border. Some of these are as small as 2,632m2; others have more bits of Baarle-Nassau within them, so that you get a bit of the Netherlands inside a bit of Belgium inside the Netherlands.
Over the years this has led to all sorts of absurdities. Strict Dutch laws on restaurant opening times reportedly led to a nightly ritual in which, at the appointed hour, waiters would forcibly move lingering customers to new tables on the more liberal Belgian side of the border.
Today that's not a problem: close relations between the two countries, plus the European Union, mean that it doesn't really make that much difference if you and your companion are in different countries when the desert trolley rolls around. But to make sure you know where you are, the two municipalities mark their boundaries with tiles, and their houses follow different numbering styles and often feature national flags, too.
Incidentally, this story contains examples of both enclaves and their slightly more obscure cousins, exclaves. The word "enclave" describes the relationship between a parcel of land and the single territory that surrounds it; the word "exclave" describes its relationship with the territory it actually belongs to.
So Kaliningrad is an exclave, because it's part of Russia, separated by other states. But it's not an enclave because it's not surrounded by a single state.
The Vatican, meanwhile, is an enclave, because it's surrounded by Italy; but it's not an exclave because there isn’t a bigger Vatican territory it's been cast off from.
Much of the land in Baarle-Hertog can accurately be described as both enclave and exclave. Don't say we never teach you anything.