Portions of the open space should be developed to afford both passive and active recreational opportunities. Passive recreational activities may include, but are not limited to, pedestrian paths, sitting areas and naturally preserved areas. Active recreational areas may include, but are not limited to, such facilities as swimming pools, tennis courts, bicycle paths and play fields but should be carefully located to avoid problems of noise, lights and similar nuisance elements affecting residential units. They shall be located not less than 50 feet from any boundary line.