This is a great winter hike in South Mountain and a wonderful option for introducing young ones and visitors to the beauty of South Mountain. Finding the trailhead is a breeze--just turn south on 24th Street from Baseline and the road essentially dead ends at the trailhead parking lot. The lot can accommodate about 30 cars, but there is "overflow" parking in the surrounding neighborhood (please obey and posted resrictions, however). There is a shaded picnic table at the trailhead, but no bathroom facilities.
The hike begins climbing right out of the shoot, as you will gain most of your elevation in the first mile. I've taken my eight and nine-year olds twice, and they both did fine. We brought our little chihuahua mix, and he also handled the trail just fine. Just take it easy and know that the elevation won't last too long. At 0.3 mi, the trail levels out just a bit, and this is a good place to take a break and turn around to enjoy the impressive views of the city, Piestewa Peak, Camelback Mountain, the McDowells, and even Four Peaks off to the Northeast.
Once you've caught your breath, continue the upward ascent. At about 1.1 miles, you finally "top out" and come to the intersection with the "Mormon Loop" trail, which is marked and heads off to your left (East). Don't take that left! Just keep going straight (South) for another 0.2 miles where the Mormon Trail dead-ends into the (signed) National Trail.
You've now completed the "stick" of this lollipop-shaped hike and have a decision to make: whether to take the lollipop loop in a clockwise or counterclockwise direction. I recommend taking the loop in a counterclockwise direction (i.e., turn right/west at the junction), as it is a little easier to navigate Hidden Valley from this direction. Look out for mountain bikers, who are often cruising along the National Trail! After a half mile (and just a little more elevation gain) on the National Trail, you arrive at the famed west entrance to Hidden Valley: Fatman's Pass!, which is plainly marked and right next to the National Trail. This ironically-named rock formation consists of a narrow crack in a large boulder that is about 8 feet high and 15-20 feet long. You enter Hidden Valley by "sqeezing through" the pass, which is capped on a far end with another boulder, forming a small tunnel. It has a bit of an amusement park feel in that, when you come out on the other side, it seems as if you've entered another world. The pass is always a hit with younger hikers. The rock of the pass is slick and makes a natural "slide" that is also a lot of fun to play around on. I only ripped one pair of hiking pants on it :-0. All in all, Fatman's Pass is a great place to take a break, refuel and just enjoy this entry to one of Mother Nature's playgrounds.
Once done playing/resting at the Pass, continue on into Hidden Valley. After hiking about 20 yards, turn around and look for Fatman's Pass and you'll see why I recommend taking the loop in the counterclockwise direction--namely, it's not very obvious where the pass is if you are approaching from the East and don't know where it is.
The Valley is about 0.5 mile long and there are numerous trails going through it. You can't really get lost, so just continue down the valley and feel free to follow whichever path suits your fancy. There are lots of little caves/nooks and tunnels to explore in the valley so feel free to take your time exploring. This exploring is usually why our trips end up being about 4 to 4.5 miles long rather than 3.5.
The exit from Hidden Valley is as spectacular as the Fatman's Pass entrance. It consists of a 40 foot natural tunnel through the rock formations, and is also a fun place to spend time exploring.
After exiting the tunnel, continue 50 yards or so to the signed connection to the National Trail. Turn left (West) and follow the National Trail for 0.1 mile to the junction with the Mormon Trail, which you then follow back down to the trailhead. If you didn't enjoy the views while you were huffing and puffing up hill, make sure you enjoy them on the more leisurely descent!