There's a fascinating YouTube series called "The Most Complex International Borders in the World" about enclaves and exclaves. [1] There are even some "counter-enclaves", e.g. a part of the Netherlands inside Belgium inside the Netherlands. [2]
[1] https://youtube.com/watch?v=gtLxZiiuaXs
[2] https://en.wikipedia.org/wiki/Baarle-Nassau