There are several potentials listed on vrbo.com.

What is "the Duluth area"? If that is extended to the North Shore --  cobblestone cabins in Tofte.

Cascade Lodge near Grand Marais is wonderful:
http://www.cascadelodgemn.com 

In Duluth proper: AG Thompson House
http://www.thomsonhouse.biz/

Ditto on Cascade Lodge. And they make the BEST walleye in the world at their restaurant.

I've stayed at "Park Point Carriage House" (a VRBO place) and it's *very nice*. It's within easy walking distance of all the Park Point touristy stuff and downtown. It's beautifully decorated and very nicely appointed with cooking gear if your friends would prefer to save some money by making their own meals. It's on the lake side of Park Point and the view from the living room is really wonderful. There's a fire pit out by the beach for romantic nights by the water. It's just really nice and relaxing and classy without being pretentious.

There is a great little apartment RIGHT ON The Lake, & Superior St. obove Va Bene Retsaurant.  Only one apt that is rented by the week/nightly.  Not many know about it, so it would be a perfect place for a honeymoon, yet its right in the middle of the summer action-right on The Lake, next to Fitgers, yada, yada, yada.  Not a cabin, but....Contact Antonio at the Italian pottery shop at730 East Superior St.  He owns it.  Also owns Sir Ben's.

There's a set of cabins up at Tettegouche that I've always wanted to stay in.

If you want quaint and private, and quiet, clean and old fashioned...no granite counter tops here--- then I like the Kee Nee Tah Cabins just south of Grand Marais.  I noticed in their guest book that there have been many honeymoon couples staying there. The cabins are set in the woods and have rock fireplaces, the real kind. And although they are not right on the rocks of the lake, there is private access (you have to inquire) to the rocks and water.  No Highway 61 noise which is what I like.

Another great place is Bob's Cabins, up in Two Harbors. (You can find their web site easily with Google.) I've stayed up there a couple of times and it's WONDERFUL. The cabins are very simple: no TV or microwave, but you've got what you need to make simple meals. They've got a great little library that you can borrow from while you stay there. The owners have made a point of keeping the place simple, clean, and quiet. It's right on Lake Superior. Actually, this sounds like EXACTLY the kind of place the newlyweds would love!

The Cabins at Tettegouche are very nice, have stayed there a few times. Getting reservations for summer months may be tricky, as the cabins are pretty popular and summer seems prime time to be there. I (personally) wouldn't call them solitude, as there are 4 cabins and a hiking trail that runs right by them, so there is traffic. But, it is a lot quieter than the city and the stars are magnificent.

Gardenwood Resort has small cabins on Senic North Shore Drive, in Duluth. For that up-at-the-cabin feel! Great walking paths along the Lake.

Madeline Island rocks, I love going there. The Inn on Madeline Island rents out apartments and condos, we once rented an apartment from them that was over the post office -- which overlooks the ferry boat landing -- it was great.

This month's issue of Mpls-St. Paul magazine has a great report on places to stay, places to go, in Duluth and up the shore. I highly recommend you buy an issue and send it to your friends.

My grandparent's owned Wonderland and I spent a lot of time there when I was a little girl! Haha, that's awesome that you mentioned it!