Recently I took a high speed train from Barcelona to Pamplona. It's on the Renfre line, and I went to the train station the day before and bought a ticket. I think it was 36 Euros. The train left at 9:30 am and arrived in Pamplona at 1:30 pm. You can check their web site. Then, right directly in front of the train station is a bus stop where you can take a #9 bus (very little cost, but can't remember what) to the autobus station. Just ask the driver to let you know when to get off. When you get off the bus, you will walk right to the intersection, where you will see a modern looking building on your left on the other side of the street. It doesn't look like a bus station, it's simply an area to take escalators down to the bus station. Anyway, just ask people in the area "Donde está el autobus?" It's a 5 minute walk from where you get off the #9 bus to the bus station or less. When you get to the bus station, go to the ticket counter for Artieda and buy a ticket for the 6 pm bus from Pamplona to Roncesvalles for about 6 euros. Then you will have a several hour wait where you can eat/drink in the cafeteria or use their internet computers for a nominal amount. The bus is supposed to take one hour, but I think mine was more like 90 minutes. I would definitely recommend this method to renting a car. Less stressful for sure.