You have maybe been in Grenen, Denmark with one leg in the Kattegat and the other leg in the Skagerrak? If not, but what about one leg in Germany and the other in Denmark? Or a leg in Holland, and the other in Belgium, and an arm in Germany?
You can stand in Rudbøl, Denmark where people shop in crowns and speak Danish, and then cross over to the Rosenkranz Street, where the euro is the currency and you might have to pick up your Travel Phrasebook.
What a jog around Norway-Finland-Russia tripoint? It looks like a very short trip, but you should remember to adjust the clock three times on your lap.
In Baarle-Nassau/Baarle-Hertog you keep your tongue straight, to keep track of whether you are in Holland or Belgium.

This is why we love borders!