The Full Underdown experience from newer machine-built trail on the Connector Trail to old school ruggedness further north with a couple of scenic stops at Underdown Lake and Dog Lake.
There are no amenities at the south trailhead. Come prepared with enough water for around a three-hour ride, longer if you stop frequently. Also bring plenty of bug spray as the mosquito's and deer flies can be vicious mid-summer.
This is a solid 2.5 to 3 hour ride for an experienced rider. Actual mileage comes out closer to 24 miles with about 2400' of climbing.
Starting from the Prairie Dells Loop
parking, head north back up the road and enter the trail right where the pavement ends into gravel road. Skirt around a cable gate and take a hard left up the first ice ridge of the Connector Trail.
For the first 2-3 miles of this ride, you'll be climbing a lot with some short downhills for a little recovery. The Connector Trail ends at Horn Lake Road crossing and at the first T in the trail, hang a hard right for the climb up Octoberfest - Trail S.
The descent will be a fun mix of flow with old school rugged rocky-ness. At the bottom, hang a hard right onto a doubletrack trail that will lead you to some primitive campsites and Underdown Lake / Camp 2 - Trail SS on your left. For the next few miles, you'll be treated to punchy climbs with short descents typical of Underdown country. Toss in a few wooden features and bridges along Yin & Yang Loop - Trails U, W & F before hitting the climb up Roundtop & White Lightning - Trails G, H & I.
After the Roundtop climb, be sure to stay right at the signs of M and H (take H to the right) to continue north to Trail LL. You'll be on a bit of doubletrack heading into Trail LL so keep your eyes pealed for the trail sign as it can be easy to miss. Trail LL will be a little more tame than what you've already experienced so take the time to recover. LL will dump onto a grassy doubletrack before linking to Trail L which is part of the Ice Age Trail.
This has been recently logged over so it can be brushy but further along you'll be high up on a ridge with nice views off to your left. Shortly after crossing Loop Road, you'll roll by what is left of the stone foundation of Bill Underdown's homestead on combination of doubletrack into singletrack Trail KK - Bumpy Bog. Exit Bumpy Bog to Trail A for some more techy climbing and a fun serpentine wooden feature, and you'll finally be at the north trailhead.
Head to the east side of the parking lot where you can reload your water from a hand well pump and take a break for a bit if needed. To continue, ride back to the west side of the parking area to hit Trail Z for some of the harder (at this point) steep, root-strewn technical climbing and descending. Z is short but will work you if you're tired.
Drop onto Loop Road for a short bit to Trail B, C, and CC. Here, you'll have some longer climbs follow with longer, fast and fun descents eventually landing you right on the shore of Dog Lake. Stop and take in the view before continuing onto Trail E and be mindful of the hard right hander onto Trail U. Drop down into Blackwater Bridge and now you're on the final stretch. Pay attention again to stay right on Trail T then a quick left/right on the Doubletrack Connector
to continue on Trail T. Some of this will be faster doubletrack and don't overshoot the left hander back to the start of Octoberfest and eventually the Connector Trail.
Now it's mostly downhill back to the lot. Enjoy the machine-built descending on your way back to the parking lot for beer and high fives. If you didn't bring beer (???) head back into Merrill and the Sawmill Saloon for some great local craft beer selection.