ATMs (Automated Teller Machines) are a terrific tool if you need access to cash in your bank account. In most cases, using the ATM at your bank is free. However, using an ATM at a bank that you don't have an account with can cost you quite a bit of money. The fees for most non-members is going to range between $2-4 per withdrawal. Then, you will get charged by your bank another $2-4 for using someone else's ATM. So your $20 withdrawal can cost you $24-$28.
These fees tend to be the highest at airports and gas stations. Save the money and avoid using the ATM anywhere aside from your own bank.