Cornerstone Park is a nice place to visit where you can be with nature but not get away from the city.
Located in Henderson, NV, it consists of a lake and a marsh. There are two walking/biking trails (upper and lower) that goes around the lake/marsh where you can see the wildlife. There's also a basketball court and a volleyball court, as well as a picnic area with restrooms.
I really enjoyed just getting away from it all here.