I usually just ride wherever I feel like for the most part, but have a 3 fun century routes and tons of loops and out 'n backs.

Centuries/Longer rides:

(out and back) Duluth - Beaver Bay - Duluth. Don't do it in fall. Leafers with RVs are on a rampage. Elderly folk don't take kindly to slowing down for bikers or even putting their fold-down stairs up (I shudder when I think of catching some metal stairs in the back of the leg at 55mph). Shoulder is crap for a couple miles.

(loop) Duluth - Two Harbors - Pequaywan Lake - Duluth. Head up to Two Harbors, north on Hwy 2 to 14/cty55, then take cty44/Pequaywan lake road to Jean Duluth, which will bring you out by UMD. (make sure you map this one out ahead of time because my directions are not perfect and there is nothing for miles upon miles and a wrong turn would suck). Very few water stops. No shoulder for a good portion, but beautiful country. I did this one while exploring, hoping something would link up eventually, which it did.

(out and back) Duluth - Munger Trail - Willow/Kettle River and Back.

Other fun rides:

Over the Bong bridge to Superior for Anchor Burger or pizza and beer at the Thirsty Pagan.

Highland Street (West End). Bottom to top of hill, one street. (best if done on fixed/ss for maximum burn/puke factor).

The old railroad grade above the Munger Trail from West Duluth to Ely's peak. I've done the ride to Ely's Peak offroad on a road bike. After Ely's peak the trail turns to 2" rocks and is nearly impossible to ride without MTB tires (unless you like pinch flats).

Skyline from Becks Road to Seven Bridges Road. (be prepared for a hill workout and gravel).

Park Point at night in the winter. Right now you can cross the bay over to Superior.

Over to Oliver Bridge (far west end), up through Superior, back to Duluth over Bong bridge.

Plus tons of others.