When most people envision the outdoors they see mountains, rivers, lakes, hot springs, an array of wildlife and wild flowers. So many forget that nature exsists in our own backyards. In many cities there are miles of trails for you to hike and enjoy the local flora and fauna. Check out the links below to see what might be in your neck of the woods.
Ridge to Rivers: Boise
Forest Park Wildwood Trail: Portland
Salt Lake City, UT
There are so many more than what I have listed here. Be adventerous and try to find your own paths. Happy hiking!