Real estate
Real estate will always tend to increase in value because nobody is making any more of it. Ever. This is not true of human beings. Supply and demand.
Decades of "land preservation," however nice it might be, took a hell of a lot more real estate off the market. It's staggering to look at a map of how much of the U.S. is held by the Federal, state, and local governments. While some of this land is accessible to industries like logging, grazing, or mining, not much of it is used for housing.
Add to that building codes that restrict density and many other things (I can't add a room to my house), and it gets even tighter.