Baarle-Nassau and -Hertog have a unique situation, because they consist of more than 30 ‘enclaves’. This means that there are parts of territory that are completely surrounded by the territory of another land. The 22 Belgium and 8 Dutch enclaves (of which 7 are officially exclaves, because they lie within a Belgium enclave) make for a situation that you will not find anywhere else. In fact, it is possible to enjoy a drink on a terrace with someone, while that person is in another land.
The situation arose around the year of 1190, when the rulers of the provinces in The Netherlands and Belgium exchanges pieces of territory as part of negotiations. Several parts of territory were exchanged, which resulted in pieces of land being entirely enclosed by another land. Since the enclaves were created, there have been a lot of attempts to solve the saturation. However, these negotiations were never successful. That is why, as of today, the situation is still the way it was created around 1190, and that is what makes Baarle-Nassau and Baarle-Hertog unique.