Easy. An accessible ΒΌ mile boardwalk leads through a break in the Badlands Wall known as "the Door" and to a view of the Badlands. From there, the maintained trail ends. Travel beyond this point is at your own risk. Watch for drop-offs.
From I-90 take exit 131. Trailhead is on left just past entrance.
http://www.tripleblaze.com/trail.php?c=3&i=6596