The trail has a vault toilet and parking at the Happy Hollow Campground, parking south of the Goreville trailhead at the Boy Scout Trail trailhead, and some parking at the trailhead south of the Blackjack Oak Trailhead. Neither of the latter two have any facilities beyond parking, however.
There are multiple points of access for Happy Hollow Trail
. You can access it via Fern Cliff St. in Goreville, IL (parking can be found just a little ways south at the trailhead for the Boy Scout Trail), in Ferne Clyffe Park itself at the Happy Hollow primitive camping area, or at a trailhead just a short drive south of the north trailhead for the Blackjack Oak Trailhead. Only the trailhead at Fern Cliff St. in Goreville will result in the "true" length, however. If you join the trail at either the Happy Hollow camping area or the more northern trailhead, the loop will only be about 4.5 miles, assuming you don't take the shortcut that removes a portion of the southernmost loop.
The descent from the Happy Hollow Campground is a rather impressive 15+ percent grade. Keep a little fuel in the tank for that climb on the way back. The trail from the Goreville Trailhead is a longer, more gradual grade. The trailhead south of Blackjack Oak Trail
is quite a bit milder.
Once down, I always go counter-clockwise along the creek, but clockwise also works. You'll have one easy crossing of the creek.
The four-way junction at the north end of the loop is the join point for the River to River Trail
, the Goreville Trailhead, and the two legs of Happy Hollow itself. It's easy to get turned around here if you're coming counter-clockwise from the Happy Hollow Campsite Trailhead. You'll want the leftmost trail, the one turning almost due west. If you go due east from this junction, you'll hit the trailhead south of Blackjack Oak Trail
Along the west side of the loop, you'll encounter a nice little stone arch, which is best first viewed coming clockwise around the trail. Going clockwise will also allow you to climb the steepest portion of the trail, the far southwestern edge. Take this portion with caution, it can be tricky.
Once you've passed that section, continuing counter-clockwise will put you back on mostly flat, level ground. This is going to be the muddiest portion of the trail, with frequent areas that are going to have standing water/small trickles coming down from above. If you're steady/have good trekking poles, you can get through here without making a complete mess of yourself.
This flat area will take you back along the creek bed, with a single easy crossing to bring you back to the east side. The trail back to the Happy Hollow parking lot is marked by a "Primitive camping" sign with an arrow. The trail prior to that is to the horse camping area.