Memory of London
On one of our first trips to Great Britain, the city of London was naturally number one. And anyone visiting London as a tourist cannot miss the main sights: Tower Bridge, Buckingham Palace, St. Paul's Cathedral, Trafalgar Square, the Changing of the Guard, and certainly Big Ben, part of the House of Parliament. It was mid-August 1976, and we were lucky!
A sign next to the entrance door of one of the corner towers of the House of Parliament announced that a tour of the House of Commons, the British House of Commons, would take place.
We couldn't let this opportunity pass us by. Indeed, together with a few other tourists, we visited a number of halls, rooms, and corridors. We sat on the Prime Minister's couch and looked at the wool sack under the Speaker's chair. And also the lectern with the two crates where the lengthy speeches were delivered.
But in one of the corridors, we saw a post office. Next to one of the counters stood a card rack, so we bought a few cards and stamps from the machine. But when we wanted to have the cards stamped, we were directed to the mailbox further down the road. That wasn't the intention! I really wanted a stamp impression from this post office. So I took a new card from the rack, wrote on it, and: handed it in as registered mail.

That cost me 52p, but I was happy to pay it. As usual, two blue stripes were placed on the postal item: a box for the stamps, a box for the registration slip and possibly the sender, and a box for the addressee. Because the postmark on the stamps did not come across well, I asked for another impression, in the fourth box. That was done properly.
After paying the 52p, I also received a delivery receipt, and upon returning home, I had to go pick up the card at the post office. Still, a nice souvenir of our first trip to London. Do you ever go to a post office when you are on vacation?

I know someone who sends himself mail from the prisons he regularly “visits”. Those can be nice mementos, too.
Certainly, and it always leads to fun stories and misunderstandings. But I don't do it as extensively as you, Cees; I just buy some stamps.