Another one of Northern Ireland's massive spanning beaches, Portstewart Strand is a two-mile long sandy beach. It's huge, and actually has a few lineups in here, due to some unique formations surrounding the beach. The Strand actually ended up getting rented out by the Game of Thrones film crew to get some shots here, if you're into that at all.
Seems to be surfable at most ends of the tide, but would probably prefer a rising, like most beaches do.
This spot is actually owned by the National Trust, which means the parking is paid. Last time I checked, it was £8.50 for the day. Parking is right on the sands of the beach.
Public outdoor showers are just down from Harry's Shack.