There are areas such as The Beacon Country Park, Three Sisters Park, Pennington Flash, Carr Mill Reservoir (which is between Wigan and St Helens). There is also the grounds around Haigh Hall and quite a few parks
There is also wigan canal, which can take you for miles. Haigh Hall is really nice as well. The Beacon is a really good area for walking. Also rivington pike. Which is only 20 mins away. You can either walk round the resevoir, up to the pike or round the chinese gardens or all 3 lol