If it is a DEBIT card that would not be a cash advance, that would take the money directly out of your bank account. If it is a CREDIT card that would be a cash advance if you use it at an ATM. The cash advance usually has interest accruing on it right away which is why people suggest using a debit card instead.
Some banks and credit unions do charge a fee for debit card use so ask specifically about that. My credit union charges 1% for use internationally. Some banks charge 3% or 5%, so find out ahead of time. If you are not traveling soon, you might want to open an account at a credit union which may have lower fees. Use that account for your travel account.
I also saw your post on the London transportation thread about the hotel you are staying in. Just wanted to make sure you had checked Trip Advisor reviews which look pretty bad for that one. Not sure how soon you are traveling and whether you can change or not without penalty.
editing to add: Wow, 3 people were posting while I was thinking, lol. Some of my advice is repetitive but I'll let it stand.