FOREX is not dealing with RUB at the moment because of the war in Ukraine.
In Spain, cash is more common than card payments, but most hotels, restaurants and shops accept card payments. In small shops and towns, cash might be a better option. There are plenty of ATMs available.
Tip! Bring both cash and card. For bus, taxi and on the beach cash is needed, but in shops and restaurants cards works fine.
Delivery to nearest post agent
Save the receipt and change back for free
Buy currency in advance, no need to search for ATMs