With Bitcoin growing popularity many Bitcoin-related services are spreading.
An important service that is spreading fast is buying Bitcoins with cash from ATM machines. But not only buying, many of this ATMs offer also Bitcoin selling.
Basically, when you Buy from Bitcoin ATMs, you insert cash in the ATM and get back Bitcoin directly into your wallet. When selling you will be sending bitcoin to the ATM address and get back the cash. Of course, in this case, you may have to wait maybe an hour until your transaction is confirmed.
Here it is an example showing how it works:
You can find a complete list of ATMs near you at https://coinatmradar.com