Where are good places to exchange dollars for euros in Sevilla?

Do not exchange cash. You get a much better exchange rate by using a debit card to get money from an ATM.
Sydney is RIGHT, debit card works best, you don't have to CARRY all that money around. Make sure you tell your bank what you are doing.
Good luck and have fun. Hubie
pqr:
At the back of your ATM card, it shows the networks your card belongs to.
If you use one of their ATM machines, the charges will be minimal.
Also for safety, use an ATM in a bank and not one on the sidewalk.
ATMs will give you the best return that a private individual can get.
Hopefully you don't have a greedy bank that charges for ATM withdrawals, but even if your bank is one of the greedy ones, you'll do much better using an ATM to get money than exchanging cash.
Credit cards will also get you a good exchange rate for buying things and services, but don't use a credit card in an ATM.
Also, if a merchant offers you the option of charging your credit card in dollars or pesos--DON'T let them charge you in dollars. It's called dynamic currency conversion, and it will give you a very bad exchange rate--with the merchant and his bank pocketing the difference.