A friend has an American Citibank account and is visiting Barcelona. How does one determine which banks, will minimize the cost of withdrawing cash? Concrete examples with supporting links are appreciated.
It depends what types of accounts you're on, where you're going (as you said, Barcelona), the exchange rate the intermediate bank uses, as well as any transaction fees (depends on your account and the foreign bank).
Transferwise is often cited as a fantastic source of how to transfer money between Aus and NZ (in my circles), and they have a ]fantastic in depth analysis of Citibank accounts and how to minimise transaction costs](https://transferwise.com/us/blog/citibank-foreign-transaction-fee).
I'd quote from the article, but as they say, it depends a lot:
If you’re planning on paying for your trip abroad using your credit or debit card, Citibank have a few credit or debit cards which can help you get a better deal on your spending. It helps to understand the terms of your specific card before you travel, so you don’t get any nasty surprises — but by choosing the right card, and following our tips, you can get a good deal on your day to day spending when travelling.
ATM fees varied widely. Caixa Bank had some of the worst I have ever seen. Banco Santander and Banco Popular were lower, but this useful list which I have copied below says they have followed Caixa into extortion. Note I have a non-EU card. The best was some minor bank in a side street whose name I don't remember, sorry.