Recreational uses such as tennis courts, swimming pools and other similar activities operated exclusively for the use of private membership and not for commercial purposes, provided that no such use, structure or accessory uses are located closer than 50 feet to any adjoining property line unless such property line fronts a public street or water way with rights of way not less than 25 feet, in which instances the required setback need not exceed 25 feet and, provided, further, that all such facilities must be located on a site having a minimum of two acres.