I searched furiously for Churaumi in Uchina – as indicated in the postcard – but I failed to find such a place.
Language is a boundary, and the further we travel from the base of our own language then things become a lot more alien. It turned out that Uchina is the local Okinawan language word for Okinawa itself. “Churaumi” was selected as the name of a aquarium in Okinawa by public vote amongst Japanese people. “Chura” means “beautiful” or “graceful” in the Okinawan language, and “umi” means “ocean” in Japanese. This aquarium was once the largest in the world, and is located in Motobu in Okinawa.
I couldn’t locate exactly where this photo was taken. I did discover that the photographer Junko Hirai had published collections of local photography: http://mickmc.tripod.com/books.html

References
The official website of the aquarium – https://churaumi.okinawa/en/
Sample of Okinawan Words and Phrases – http://www.okinawan-shorinryu.com/okinawa/uchina.html
The traveler’s guide to Okinawan dialect – https://matadornetwork.com/abroad/the-travelers-guide-to-okinawan-dialect
Okinawa Churaumi Aquarium – https://en.wikipedia.org/wiki/Okinawa_Churaumi_Aquarium