Kos has a long horseback riding history and to this day the St. George Riding Club in Pili meets once a week on Marmari beach. Riding began with the advent of Christianity on the island, and this non-profit organization offers riding lessons as well as a group to go riding with. Marmari beach is 30 km long, with sandy shores that are a favorite for the locals. Kids are part of the group and rides end with both horses and riders in the water.
There are a number of other riding clubs on the island, so ask the locals for their personal favorite.