It's a real problem right now.
The only thing which on the long run makes sense are World index ETFs.
Real estate in western EU -> No return, highly speculative if it ever will give good returns.
Bonds -> Low risk bonds, useless
Gold -> Didn't really deliver
REITs -> They don't behave like real estate but more like stocks, whats the sense of buying them?
Real estate in other countries makes sense, but maybe through open Fonds than REITs.
Dubai:
AFAIK the price of the real estate doesn't really increase (as we are used to), so you might be stuck with an investment which won't go up in price.
They have a full empty dessert for building new real estate. They are not limited by space in contrast to the center of London, Paris.