It's not a "special place" exactly, but a special experience...ride the U.S. Mailboat on the lake. If you're going to be there in the summer, of course. http://www.cruiselakegeneva.com/walworthmb.php

bjl, thanks for the recommendation. I have heard of this and it sounds fun.

I live and work in Door County - there are so many great restaurants and hotels ...
check out www.foremostresorts.com ... 4 differnt lodging establishments, many pricing options and differnt locations up and down the peninsula.
Have fun!!!

Recently also driving up from Chicago...
We stayed at the Wagon Wheel at Rowley's Bay which is well known. There is a fish boil out front which is a Door Co. thing. Another unique site is that restaurant with goats grazing on the roof...Al Johnsons. Lunch also at Julie's Cafe-Fish Creek. We took in several entertainment spots: Peninsula Music Festival and Door County Theatre. Also lots of art shops to browse as your drive around.
Bill in Boston

Thanks for the great info Denise_Stillman and Ozarksbill.

Not sure how long you'll stay but here's what I've got. I spend at least a weekend or two in Sister Bay every summer so I know the area fairly well!

Along 42 in Door County, Fish Creek has a great downtown shopping area near the water. Moving north, check out a drive-in movie at the SkyWay Drive-in, get some DELICIOUS ice cream at Wilson's in Ephriam, and I'd highly recommend staying at Ephriam Shores. Been there many times, great location and restaurant attached as well. Seaquist in Sister Bay is a great place to get tasty jams and downtown Sister Bay also has some great restaurants and shops. If you're looking to visit the beach or a park, Peninsula has Nicolet Beach and tons of amenities (like bike and boat rentals, etc), as well as a lookout tower you can climb to get a great view of the entire bay. Newport and Bailey's Harbor are the other two parks I'd recommend, especially for swimming (on a good day). Finally, if you have an extra day, head up to Gill's Rock and take a ferry up to Washington Island - lots of fun things to do up there. Wish I could give suggestions on Lake Geneva - went once with my grandparents when I was little but haven't been back. Have fun!!

Couple more lodging suggestions for door county... though I haven't spent much time in the town itself, Bailey's Harbor has a few good hotels - I've heard the Blacksmith Inn is wonderful. There's also some really nice properties on Kangaroo Lake as well. The wonderful thing about Door County is that all the towns are within minutes of each other, so no matter where you stay you'll have access to a cute downtown area, and plenty of other options within 10 minutes.

Other "up-north" things that I forgot include mini golf - Pirate's Cove in Sister Bay is good and there's a slightly cheaper option literally next door whose name is evading me at the moment.. Johnson Park I believe? - and the confectionary in Ephriam. Really, I'd highly recommend staying there, especially because there's a bunch of waterfront amenities across from Ephriam Shores as well, and a bunch of cute shops in between Ephriam and Sister Bay. Fish Creek, Egg Harbor, Ephriam and Sister Bay are where I'd recommend spending the most time - but that' just me!