Lookout Rock is a large rock outcrop on top of a small hill overlooking the Horse Thief Campground, the valley below, and the peaks and rocks in the NW corner of the Black Elk Wilderness.
To get to the cache, follow SD Highway 89 and turn west on FS 352 until you get to the parking coordinates listed below. From there, follow the trail on foot to the cache. Even though this trail is an "official" FS road, there is private property south of the trail, and a gate about half way to the cache. That's where the "official" road ends, and driving past that is not allowed per Forest Service regulations. So in the interest of maintaining good relations with those nearby property owners, don't drive this. The entire route to the cache and back is on BHNF public land, however. Once you get to Lookout Rock, you will need to do some steep climbing and rock hopping to get to the cache, which is hidden along the edge of a short cliff. You are looking for a small lockable container with standard logbook and some swag. It's large enough to hold a couple of smaller trackables.
Please re-hide the cache as good as you found it, and enjoy the view from here.