Cavern Inn '72
The ultima of our family trip in the summer of '72 was that classic destination, Carlsbad Caverns NP. The cave was impressive, of course, but I was 11, so just going to stay in a motel somewhere was fun. We ended up at the Cavern Inn Motel in Whites City.
The back of the card is incredibly busy, with bullet-pointed lists of motel amenities (including "clean mountain air" and "sky ride to Indian Cliff House"), information about the national park (hours and admission), and a map. There's barely any room to write a message on the oversized postcard.
I was glad to learn that Carlsbad Caverns charged $1.50 admission at the time for everyone over 16, which means my visit didn't cost anything. These days, over 15 admission is $6 for admission without a guide, which is what I think we did, so in real terms cave admission is cheaper than it was in the early '70s, since $1.50 in 1972 equals about $8 now. That's assuming the card wasn't that old when we got it, which is a fair bet since it's got both a zip code and an area code on it, and besides, look how important orange and aqua are to the color scheme.