It isn't hard to get to Pamplona - though train connections from the Basque Country are poor, buses from all over the country will get you to Pamplona, while there are regular trains from Barcelona, Madrid and Zaragoza. There is also a local airport (for internal flights only) and international airports in Bilbao, Vitoria and Zaragoza (as well as, of course, Madrid and Barcelona).
But with accommodation in such short supply (and extremely expensive when it is available, there are other factors worth bearing in mind. Read more: What's the best way to see the Running of the
Once you've decided how you're going to view the festival, check out these links below:
How to Get to Pamplona for the San Fermin Festival
Where should I stay for the Pamplona Running of the