Definitely not the restaurant business.
A small investment property in a strong location would probably be your best bet. it's not as simple as it sounds though.
The best way to approach the restaurant business is to buy one on the cheap that someone is selling. Then fix it up, hopefully DOUBLE your investment, then SELL!
It befuddles me how many people post on Covers about opening up a restaurant, yet don't realize how much of a money pit it usually becomes.