An hour at what speed?
For a beach to the north, Caernarfon is the best bet, but it's probably between 1:30 and 2:00. The beach is within easy walking distance though, and the scenery on the way there is great. Blackpool is great as well, in a totally different way, but that's even further.
Other nearer suggestions...
Duxford - visit the museum.
Leicester - I've been told there's a go-kart track next door to the airfield.
Cambridge and Norwich - quite nice cities for a random day trip.
Elstree - visit London.