Real estate and rent, just like bitcoin, designer fashion, "art work", and watches. Unfortunately, you need somewhere to live. If it's more profitable to hold empty real estate than or less dense/improved property waiting for it to go up then that's what will happen.

If people can effectively speculate on something in a leveraged high liquidity environment, they will, and prices will go up. Look at the terrifyingly overbuilt real estate in China with pricing comparable to NYC or London and huge vacancy rates.