The trail is great for those with at least a little experience handling obstacles such as rocks and logs, as it is full of them. The really nice thing about this trail is it starts easy and gets progressively more challenging throughout its length. If you're a beginner, you can turn off and climb out or repeat the easy and/or intermediate sections. If you're more skilled (or hard headed) you get a break before the rough stuff the next time around. I've replaced my rear triangle, dérailleur, tires (to say nothing of tubes), etc. because of this trail; it will beat you and your bike up.
Take 18-151 to Blue Mounds, west of Madison. Go north on Highway F, left on ID, north on Blue Mounds road to the park.
http://www.singletracks.com/item.php?c=1&i=2548