Perhaps one of the hardest places to get to in the Keweenaw, Keystone Bay is a solid hour's drive down less-than-maintained dirt roads and logging two-tracks. And that's on top of however long it takes you to get to the end of US-41. It's entirely worth the journey though, and I'd say this is one of my favorite places to camp in the area.
The bay consists of a mostly sand beach over much of its length, with the eastern end of it turning to rocks after Union Creek. There are three main camping areas around the bay, each of which are in the woods by the beach and relatively large; big enough for two or three separate parties of 6-8 to pitch tents and still be separated from each other. The photos here were taken during a nearly record high lake level, so on lower years you can camp right on the beach if you want to. At the central camp area there's also an improvised toilet. It's no outhouse but it's better than a log.
To get here, take US-41 north through Copper Harbor until it ends and continue on Mandan Road. Drive Mandan Road for 6.6 miles and turn left onto an unmarked dirt road. Drive a quarter mile and turn right. Drive a half mile and turn left. Drive a little ways and you'll get to a yellow gate. If it's locked, park here and hike the two track to the beach (~0.6 miles). Otherwise you can drive through all the way to the lake and the westernmost camp area.
You should be able to make it down the dirt road sections in well less than an hour if you have a suitable 4x4 with good clearance. That being said, do not attempt to get here in a sedan or a minivan. You will be bottoming out left and right. If going to the central or eastern camping areas, you'll have to cross a stream or two. Lastly, try to get your firewood deep in the woods instead of near the camp areas. The DNR has postings up threatening to close the area if the "destruction and littering" continues. Probably won't happen but you'll find better dead wood the further away you go.