Without traffic Catoctin Mountain about an 80 minute drive from the District. if possible, you want to get there early on weekends (before 10am) as parking can become a problem.
A link to the trail map is provided below.
This particular hike is fairly strenuous (there are a fair number of rather lengthy hills) and is not appropriate for young children. Check out the Catoctin Mountain hiking page (link below) for more information on shorter hikes. Longer hike options are available as well.
Whatever hike you choose, make an effort to stop at Cunningham Falls.
The trails are not terribly well marked, but there are signs along the trail offering directions and distances to various landmarks. Make sure to bring your map and keep an eye on these signs and you should have no problem keeping on track.
Pets are welcome but must be leashed.