Why we love it: The seclusion. This is the longest trail in the park, it's not kid-friendly, and you can't bring dogs, so traffic is minimal.
When to go: Morning or early afternoon. Allow two to two-and-a-half hours round trip.
Castlewood Canyon State Park is a family-friendly spot: Several of the trails are short, paved numbers that are perfect for strollers and young children. A jaunt here can easily be turned into a school lesson: View ruins of the original Castlewood Dam (which burst in 1933, sending a 15-foot wall of water toward Denver) on the Dam Trail, remnants of the historic Lucas ranch on the Homestead Trail, or a waterfall on the Creek Bottom Trail. My favorite though, because of its terrain and remote feel, is the East Canyon Preservation Trail— a four mile loop navigable in some places only by cairn rock piles. 
From the moment you step foot on the trail, the landscape immediately teems with cactii, scrub oak, and mini-monoliths. Several rare species of flora grow here (which is why it's not a good choice for kids and pets). A number of small creatures call this area home, too: lizards, chipmunks, rabbits, and blue jays can be spotted in abundance. A half mile in, you'll get your first view of the canyon. Continue on, following the cairn piles, and eventually descend onto the cool canyon floor.
I took my surroundings in for a few minutes before continuing on, and enjoyed the gentle gurgle of Cherry Creek before crossing a wood pedestrian bridge. After a short woodsy section, things get more technical and I had to scramble up and over a few boulders. A mile and a half in, there's a sign for the canyon loop (a 1.14-mile trail that winds around a rocky plain). Definitely take the loop as it's the best part of the trail. Since much of the loop doesn't have a path at all, I felt like I was in the old West and following the clues the land (and previous visitors) gave me. In reality, the trail isn't far from civilization, but it was fun pretending.
The loop drops you off by the creek again, then it's another 1.4 miles back to the parking lot. You can move a little faster on the return trip, since the terrain will be more familiar. But watch your footing. I almost bit the dust a few times while jumping from rock to rock.
Getting there: Take I-25 to Castle Rock and exit on Founders Parkway. Take Founders Parkway east to Highway 86, then drive east on Highway 86 for four miles to Franktown. Turn south on Highway 83 (South Parker Road) and drive five miles. Castlewood Canyon State Park will be on the right.