The postal service, both in the US and elsewhere, makes their best effort to deliver mail, despite how difficult we make it. Some deliveries are just short of miraculous!
1. A postcard from Krakow that was addressed to:
nevertheless made it to its destination. Local postman Paul Gardiner knows his houses... and their doors!
2. Paul Bates didn't know his friend Peter O'Leary's address, but knew where he lived, sort of. So he addressed a Christmas card with a map! The card somehow arrived at the right office in Cornwall, where a postal worker recognized the name, and the card was delivered—in time for Christmas.
3. Where I live, people without stamps sometimes put change in their mailbox to buy stamps from the mail carrier. That's hard to do if you don't have a large horizontal mailbox. What happens if you just attach the money to the letter instead of a stamp? This guy tried the experiment.
4. This postcard had a proper address, and proper postage, and it made it to it's destination ...90 years late!
5. Manuagua, Nicaragua stopped using formal street addresses after the 1972 earthquake leveled much of the city. Now, letters find their way via a local system that gives directions and landmarks on letters and packages. An example:
Donde fue Lacmiel, 2 cuadras arriba, 1/2 cuadra al sur (translated: where previously was located Lacmiel 2 blocks east, 1/2 block south).
6. If you are looking for a different way to mail a letter, you could mail one from underwater. Yes, there are post offices and mailboxes underwater. Gadling lists five of them. This Post Office is off the coast of Vanuatu. You could also mail a postcard from underground at Carlsbad Caverns.