Port Lockroy is a historic site on Goudier Island in Antarctica, originally established as a British research station in 1944 during WWII. The station operated until 1962, and in the following decades, it was preserved as a museum and heritage site by the UK Antarctic Heritage Trust. It has a museum, post office (that works!), and ongoing conservation efforts to maintain its historical significance. At the post office, you can send postcards and it will take 3-6 months to reach their final destination world-wide.