Well, no details in re. the festival, but getting there is straightforward enough:
On foot - go down Lake St (off the Abigdog Rd) and right to the end of it. Over the bridge over the lake then over the bridge over the railway.
Follow the path, known locally as the Devil's Backbone and you'll find yerself in the pub garden before you know it.
By car - Southbound on the A34, past the golf course there's an unassuming turn off to S. Hinksey village. Follow the road round and then spend a short while driving around the village to find the pub (nb. it's not a very big village).