The currency in Costa Rica is Colones. It is not exactly the easiest conversion as $20 is around 12,250 colones. If you want to get money from the ATM you can get American Dollars or Colones. Note that the fees are very high. You are going to have to pay a $9 fee just to use the ATM then likely another $5 fee from your bank. Even if you are rewards member at your Bank like Bank of America or Wells Fargo, you are not going to get these ATM fees refunded like you would in the United States.