Walk on the beach (tide permitting) down to the Tide Restaurant and back (about 45-60 min). Then if anyone is willing, up to Red Rock Park and back (about another 30 min).
Just off the rotary there is a small parking lot with a playground and building next to it. Meet on the ocean-facing side of the building. If the lot is full, you can drive a bit further up Lynn Shore Drive toward Swampscott and there is free street parking.