DIRECTIONS:  From Denver, take I-70 east to Peña Blvd.  Head north on Peña, towards the airport, and exit at 56th Ave.  Turn left (west) on 56th and look for the large parking area and trailhead on the right.
The First Creek Trail is one of the most scenic trail in the Rocky Mountain Arsenal National Wildlife Refuge.  The trail explores the western edge of the refuge, far away from the visitors center and the more popular trails like Lake Mary.  That's not to say that this trail is unknown, in fact it's a very popular trailhead for hikers and bikers. 

The trailhead is in the DEN open space managed by the City of Denver and the Denver International Airport (DIA), in fact, this hike is probably as close the DIA as you can get...but still very far away...

The trailhead serves both the First Creek Trail and the Perimeter Trail (which follows the entire perimeter of the refuge) and therefore sees plenty of traffic.  However, most visitors stick to the Perimeter Trail and when you branch off into the refuge, the crowds thin out significantly.

Head north from the trailhead on the wide gravel road that is the Perimeter Trail.  Keep an eye out on your right for the dirt trail that goes through the open space, it's about the same color as the surrounding prairie dog village so it might be hard to spot.  Turn onto this trail and follow it through the cottonwood forest (should be amazing the in the fall).  Eventually, this trail meets up with the paved First Creek Trail, turn left (west).  The paved trail intersects the Perimeter Trail, turn right for a few minutes until you see the archway and the signs for the Rocky Mountain Arsenal National Wildlife Refuge...enter the refuge.

Now in the refuge, the narrow trail follows First Creek as it heads west when the creek reaches a scenic pond, the trail turns back east, then head north into a wide open section of prairie.  Before long you'll spot your destination, the First Creek Overlook. This structure looks over the wildlife fences into the wide openness of the refuge...you might just spot some bison.  

For your return trip, you can either go back the way you came on the first creek trail, or take the Perimeter Trail back.  The Perimeter Trail is the fastest return, but no where near as scenic as the First Creek Trail.  Either way, you return to the same trailhead.

For the entirety of this hike you are treated to magnificent views of the Front Range mountains, on a clear day.  You can see everything from Longs Peak in Rocky Mountain National Park, to Mt. Evans, and all the way down south to Pikes Peak.  Beautiful views.  This is a great trail and a nice way to visit the refuge in relative solitude.