Tripoints
Of course there is the Dutch tripoint, that was once a quadripoint.

In 2013 I visited a lot of tripoints together with Ruud.
First the three tripoints of Luxembourg.
Then the tripoints of Germany, starting with CH-DE-FR near Basel and AT-CH-DE in the Bodensee.

We continued to AT-CZ-DE en CZ-DE-PL.
Liechtenstein has two tripoints.
In 2024 I visited three tripoints in central Europe.
In 2025 I visited the tripoint of Austria, Italy and Slovenia.
A great place on top of a mountain.