I just got back from Spain on Monday June 27th, and a friend and I rented a car in Sevilla on 6/22 and drove to Ronda, where we spent the night before we proceeded on to Granada. We stayed there from 6/23 to 6/26, and drove back to Barcelona on 6/26.
I'm from the US, and I obtained an International Driver's Permit from my local AAA office in Atlanta before I left. You'll need to do this before you leave! The price recently increased from $15 to $20, and the permit lasts for one year. You'll need a valid US driver's license, along with two passport sized photos, which were taken at the AAA office. I don't know if you need to be an AAA member to obtain this permit, as I'm a AAA member, but I suspect not. After I rented the car in Sevilla I was told that I didn't need the IDP to rent the car, although I did show it to the agent, but she said that I would need to have it if I was stopped by the police.
My (German) friend and I were initially planning to drop off the rental car in Granada, which I rented from Avis, and I found out that it could be left (and, presumably, obtained) at either the train station or the airport in Granada. The train station in Granada is considerably closer to the center of Granada than is the airport. In Sevilla we picked it up at the Santa Justa train station; the office is located within the station itself. You can also pick up a car at the airport, but, again, the train station is much more centrally located.
We stayed in the Hotel Doña Maria, which is on the same plaza as the Catedral de Sevilla and not far from the Real Alcázar de Sevilla. We arrived in Sevilla by train from Barcelona on 6/19 and left on 6/22, and we didn't need a car. I would highly recommend a visit to the Real Alcázar, and we took Rick's suggestion and went on a guided tour by Concepción Delgado's colleague, who was able to purchase entrance tickets for us when none were available for sale last week.
We loved Ronda! We stayed at the Hotel Ronda, a five room hotel close to the New Bridge in the Old Town on the Calle Ruedo Doña Elvira. The manager was a lovely middle aged woman who spoke English fluently, and she recommended dinner at the Puerta Grande (http://restaurantepuertagrande.com/) on Calle Nueva next to the Plaza del Toros, the bullfighting ring and museum. Our meal was outstanding, and it was easily my favorite restaurant in all of Andalucía.
I hope this helps. Please let me know if you have any other questions about Sevilla, Ronda or Granada.
Best wishes,
Darryl M.