I created Nat's World, my immersive photo exploration game, the hard way: each picture is added into the environment by adding a line to a large Python file. It worked for me because I'm a geek, and it was quick to get the whole thing going. But I've idly toyed with the idea of building a GUI application to create similar environments. I think it would be fun to write, but I've never seriously started on it.
Redbug Technologies now has Mapwing, a commercial product to build the same type of walkthroughs. I haven't tried it, but they've got a few demos on their site. It was interesting to see that they faced some of the same problems I did, for example, how to show a simple photo of a spot without it being a fully-realized four-direction point you could navigate to. They did it by putting a camera icon on the spot before you get there. I did it by drawing a thick white border around the photo (to make it like a snapshot).