Post card
I love post offices and mailboxes.
I sent postcards every day to my little daughter waiting for me in Japan. Nowadays, we can send email from anywhere, but nothing compares to the wonder of a postcard with a picture on it.
I was able to buy official postcards with pre-printed stamps, like official Japanese postcards, at the Austrian post office. When drawing sketches, I like to use postcards from that country, so I ask if they sell them at the post office. If they don't, I buy A6-sized cards at a stationery store.
I also want beautiful commemorative stamps for my mail, so I search for a post office to get some. Even when I arrive at a post office in a big town, there are a row of counters, and it's usually not clear which one sells commemorative stamps. There should be a sign with information, but it's hard to tell which counter is which. It doesn't say "commemorative stamps." Just ask the staff.
Even if you don't speak the language, people will understand if you show them an unfinished postcard and ask for a stamp to Japan, but they'll only give you a regular stamp. I'd made the effort to find a large post office in search of beautiful stamps. Even though they didn't understand, I didn't give up. I stringed together every word I could think of, trying my best to get a variety of beautiful commemorative stamps.
However, with my language skills, it's quite difficult, and especially in non-English-speaking countries, I often struggle to get people to understand me no matter how hard I try.
Also, it seems like the number of mailboxes at airports is becoming increasingly scarce.
A small local post office in England only seemed to carry regular Queen stamps.