We did the Round House Loop Trail here (about 3.5 miles) and it was not my favorite hike around St Louis. Since it's moderately trafficked, we walked through spiderwebs the entire time. I hike all the time and have never experienced anything it before. It's also not very scenic and is not marked well at all! There are 2 trail heads within 30 feet of each other so be sure you start on the right one if you decide to go.
Did the Joseph Declue Trail today - nice fairly easy hike - had some hilly areas but not a lot - watch for horses on the trail and what they leave behind. Also had lots of bike riders on this trail. Signage could be improved especially where trails overlap. I would do this trail again
The length of the trail listed is incorrect. Its actually 16.3 miles. The trail head listed is the northern ending point, in Rockwoods Reservations. The southern trailhead, or starting point is on the north outter road on HWY 44, about 1 mile west of Allenton Road. The trail is very well marked, and allows biking in the Greensfelder park area, but not in the Rockwoods Reservation area.
The trail itself is great. It is a moderately cleared trail with spray paint markers on the trees every ~30ft. I never felt like we couldn't find the trail when hiking. Lots of hills through the area.
Of note, the trail route pictured is not the location that google maps will take you to for the south trail head.