I am enchanted by this postcard of Belem Tower from Lisbon, Portugal. I received this from Postcrossing last year. It's a UNESCO World Heritage Site, but to me it looks like a chunk of castle right on the river--in an "Inception" kind of way.
When I first saw it, I thought it was really sitting on the sea with all those swimmers just close by. This is one of my favorite postcards which I like to occasionally include in my ever-changing tabletop displays at home.