Quite a parochial one this but Donington Monsters Of Rock 1994. Basically it came right as I was starting to get into rock and metal so there was tons of press, and the whole thing went out on radio 1 (mostly live, some recorded and broadcast later). So I was reading about it, listening to it, taped it and played those tapes to death… a bunch of bands that I came to love played it- still listen to the recordings of the Wildhearts, Therapy? and Sepultura sometimes 20 years later. It had such an impact on me, maybe I’d have come round to these sounds anyway but maybe not and the love of rock and metal kind of made me.
Anyway, that’s about as formative as it gets for me, so, to travel back in time and live it would be incredible. Make this stage my rubicon 😉