It may consist of grassy areas, rocks , soil and trees , but may also contain buildings and other artifacts such as monuments , fountains or playground structures. In North America, many parks have fields for playing sports such as association football , baseball and football , and paved areas for games such as basketball. Many parks have trails for walking, biking and other activities. Some parks are built adjacent to bodies of water or watercourses and may comprise a beach or boat dock area. Often, the smallest parks are in urban areas, where a park may take up only a city block or less and is ideally within a Minute Walk of its residents.