One of my favorite recommendations is for a hotel made out of salt. We stayed at the Hotel Luna Salada when we visited Salar de Uyuni, the world's largest salt flat, in Bolivia. There's a good entry over on this blog where mikehowie recounts the experience of walking on the salt flat. He says that "standing on the crisp salt crust, formed millions of years ago, and looking across miles upon miles of brilliant white emptiness, feels like being on another planet." I don't doubt it.
Apparently, there are a handful of hotels made out of salt on the Salar de Uyuni. There aren't many construction materials out on the salt flat, so people cut blocks of salt from the Salar and build hotels out of them. It's a pretty ingenious strategy and I bet staying at one of these hotels is a very cool experience.
If the hotels made out of salt aren't enough reason to plan a visit to the Salar de Uyuni, you should also know that the Salar becomes one of the largest mirrors on Earth when covered with water