On this day in 1831, King Leopold I was installed as King of The Belgians, since when 21st July has been celebrated as their National Day. I'll leave that in English because Belgians speak Vlaams (60%) and/or Français (40%) and German (0.7%) and if I write the Flemish form first I may offend the Francophones and v.v. Presumably, today there is a holiday in all Belgium not just in the bit South of the Netherlands. (Belgium shed its colonial empire in 1960, when the Belgian Congo became the Republic of the Congo, now called Democratic Republic of the Congo.)
I say all Belgium because part of the country is an exclave surrounded by the Netherlands municipality of Baarle-Nassau. Actually there is a mess of 22 exclaves which form the Belgian municipality of Baarle-Hertog (aka Baarle-Duc although it is a long long way from Francophone Wallonia):
There are advantages. Belgians are more secular than their Calvinist Northern neighbours and so allowed shops to open on Sundays. It would be invidious to prevent NL shops in Baarle-Nassau trading when their rivals along the street could do so; so they obtained a dispensation. I also understand that there is a brisk trade in fireworks which are much more tightly regulated in NL than in Belgium. Otherwise, with the Euro having replaced Francs and Guilders, and the EU homogenising all our lives, I guess there aren't many remaining differences.
Not to be outdone, there is a single Dutch exclave South of the border: just under 3 hectares of farmland called Vossenberg (Fox mountain). I've marked it in a foxy brown below because I don't trust you to figure it out for yourself (and I'm applying for a job with the Gemeente Baarle-Nassau):