In August you might like to join in the annual Warrior's Run, in Strandhill. It starts from the seashore, up Knocknarea and back.
It should be possible to take a boat trip on Lough Gill. There is a passenger craft which will take you to Parkes Castle, near Dromahair, County Leitrim, or you could hire a boat and make your way where you will.
Strandhill is a noted surfing beach. Be warned, however, that there are treacherous currents here, and swimming is prohibited.
