As a "relaxing" sideline to US and France I collect the 1939 New York Worlds Fair (NYWF).
Like Don, I went to the 1964 NY World's Fair as a child. As a lad of 7, I was unimpressed with Michelangelo's "Pieta," but I enjoyed the half-scale(?) dinosaur models in Sinclair Oil's "Dinoland." Perhaps I should have collected that fair.
But for stamp collecting, the 39/40 NYWF is just great. The Trylon and Perisphere are visually striking on US 853, which I find one of the more arresting US issues ever given the degree of abstract clarity, for its time and since.

But that's just the beginning. There were dozens of international issues on the occasion, so many so that the NY
Sun newspaper issued a rather lengthy, but slightly incomplete chart enumerating them.
Here is just a tiny tidbit. It seems that every one of these international issues leads to fascinating historical background.
In this case, a somewhat ordinary business cover from the Dominican Republic bearing several of the Dominican Worlds Fair tribute issue. one Sc.343, two of the 3 centavo #344, and two of the C33 airmail. The return address is in the capital city of "Cuidad Trujillo," which the dictator known as "El Jefe" renamed after himself in 1936. Trujillo's visage is on the stamp in the lower center. The NYWF stamps depict the Trylon and Perisphere of the NYWF and a proposed Columbus lighthouse featured on a number of other DR stamps of the day.


Then there are dozens of interesting overprints on various of the the international issues. Some are often forged (Portuguese and French colonies in particular).
Here are two Ecuador 437 (a two centavo #388 from their multi-stamp NYWF issue, but overprinted to five centavos). These with a doubled overprint, a known variant not separately numbered in Scott (as of the 2009 and 2017 catalogues I usually use).
