Fun fact: you don't have visit the South Pole to mail a postcard from the South Pole. (But it's probably more fun if you do!) This ties in to a postcard story I told here about ten years ago.
I had missed my sister's 30th birthday and wanted to surprise her with something out of the ordinary. I learned that you can roundtrip a postcard through any US post-office, and used this to send her 30 postcards from 30 states.
I started with a list of USPS POs and looked for 30 that were in interestingly named or out-of-the-way towns. I then used Zazzle to custom print postcards, each with a picture on one side that I found on the Internet of the town or PO.
On the message side of each postcard was printed a single large letter. Once my sister received all 30 cards the large letters would spell out a message. I hand wrote a tidbit about each place after the large letter to disguise the large letter's purpose.
The cards were all addressed to my sister in FL. I stamped each card with a stamp of the state it was from, using one of the USPS's 50 state stamp collections. (The collection I used was from many years ago, but I found a sheet on eBay.)
I wanted each postcard to be hand canceled from the town it was supposed to be from. I also wanted the postcard to show up at my sister's in pristine condition. So I placed each postcard into an envelope addressed to the postmaster in that town’s PO. The envelope also included a second stamped envelope addressed to my sister, and a letter to the postmaster asking them to hand cancel the card, then mail it on to my sister in the second envelope.
Then I dropped all thirty envelopes in the mail in NC. I had no idea if this would work, but after about 3 weeks my sister received them all in FL. The envelope which traveled the farthest was round-tripped through Barrow, AK. I also sent her cards via HI and ME.
Some of the cards went through towns so small that the last name of the postmaster hasn't changed in that town for generations (the USPS website lets you look up current and former postmasters).
This was a neat project. I learned a bit of trivia about all these small towns. I learned some people collect postmarks. And tying back to my intro, I learned that you can roundtrip postcards through the Amundsen-Scott South Pole Station post office[1], but it takes about a year.
Here's what the cards looked like after she received them:
[1]: https://www.jeffreydonenfeld.com/blog/2012/12/the-worlds-sou...