The George Mitchell Nature Preserve is a nice preserve that straddles Spring Creek in The Woodlands, TX. There are some small, scenic, marshy ponds and lakes, making it an ideal spot for white and blue herons, turtles, etc., but there can also be a lot of gnats and "no-see-ums" flying around.
On the south side of the creek, there is a nice, wide, well-marked nature trail with some alternate loops. The main trail has distance markers and lettered posts so you know where you are at. The north side of the creek also has nice exercise and mountain bike trails. The exercise trails are wide and have distance markers on them, whereas the bike trails are a "tangled mess" of primitive, narrow, unmarked trails.
A section of trails are a part of the Spring Creek Greenway Project currently under development. This is one of the nicer hikes in the greater Houston area, in my opinion, as it has scenery, solitude (in some sections) and distance.