We did the Devil's Tower on our trip. And yes, it did take a long time to get there. Fortunately, we were not time-limited. While we were glad we went, but if we were time-limited, I don't think we would have done it.
Nice campground inside the park itself, though. Very peaceful, well kept and a great view of the tower as you sit by your campfire. We opted for the in-park campground rather than the KOA just outside the park. The KOA looked fair and we stopped in to check it out on our way out, but we bought coffee from them and I can say it was the worst coffee I have ever tasted. Two sips and we threw ours away. And I've been known to drink some real swill when it comes to coffee.
