Take I-75 north across "the bridge" and follow itabout 7 miles north to M-123. Take M-123 N-W to M-28 (about 33 miles). Take M-28 West for what seems like forever (it goes through the "Seney Stretch" - the world's straightest and most boring stretch of road known to mankind)about 82 miles later (no kidding) you will be in Munising. Keep driving through Christmas (no, this one's a town) and about 38 miles later you'll connect to US-41. Follow this North through Marquette, and on to Houghton, about 105 miles. If you've been doing the math this far, you should have travelled approximately 265 miles - you're now at the gateway to the Keweenaw Peninsula. Take the bridge across the canal/river and head north (you can't really get lost - it's an island since the canal was completed years ago!) Stop in the tourist office in Houghton and pick up a travel map. It shows most of the roads and some of the attractions. You can even get info on going to Isle Royale (that island off to the left of the keweenaw).
An alternate route to get to the Seney Stretch is to take US-2 West from St. Ignace. About 47 miles from St. Ignace is M-117. Take it north to M-28 (about 15 miles) and turn left onto M-28.
Either route works, the first takes you closest to Tahquanemon Falls, a beautiful waterfall pair vivid with natural beauty. The second takes you along the northern edge of Lake Michigan, complete with secluded beaches (except for US-2) and rivers. Both are worthy of the drive.