Valencia is by far the closest major airport to Benicassim, at only 86km away, it’s little more than an hour’s drive away (you may even manage sub 1 hour times if you’re a bit daft behind the wheel). You can drive , get the train, or as an added bonus get one of the special festival buses that take you direct to the festival site!
As per the above, it’s a nice quick journey into Benicassim from Valencia. You just pick up further down the E-15 than you would do if you were visiting from Barcelona, and continue in a straight line until you hit the sign posts for Beni! Easy. Unless you’ve got a really weak bladder you probably won’t even need to stop off. Check out Expedia to compare prices on popular car hire outlets at Valencia airport.
The train from Valencia will take you about an hour. The trains drops you virtually right outside the festival site – be warned it’s still a bit of a walk to where you’ll actually pitch your tent but entirely doable – say about 500 metres or so. Check prices for trains from Valencia to Beni.