IMHO, a proposal shopuld be very personal--try to tie it to something special just to the two of you.

Check with the hotel concierge. I'm sure he/she can help you arrange something. As far as where, will your girlfriend want a private moment with just the two of you or do you want it in the midst of a large crowd of strangers?

If you want someplace with scenery, the area around the Lincoln Park Conservatory has nice gardens, but can be crowded much of the day and into the evening with wedding photographers.

There are several spots in Grant Park where you could go around dusk with the skyline in the background. The Cancer Survivors Pavilion at Randolph and N Harbor Dr is usually pretty quiet and also has nice plantings. It would be a short walk from your hotel.

A limo ride at night, stopping at the planetarium for the best view of the Chicago skyline to pop the question.. ending up at John Hancock for drinks to celebrate.

We've enjoyed The North Pond restaurant; great ambiance, nice views; great food. When you call to make reservations, tell them you're getting engaged, and they'll make something special for you. We've gone there for our anniversary and our menus had "Happy Anniversary J&R" as well as a message on our dessert plates. Perhaps they could help you with some ideas. One warning: even though the address is on Cannon St., you have to arrive on Stockton street, walk under a small bridge that is somewhat uninviting, but when you come out the other side, you see the restaurant and the nice view.
It's in Lincoln Park area, near the zoo.

http://www.northpondrestaurant.com/

In front of the "Bean"? I haven't seen it except in pictures DS took.

At the Alfred Caldwell Lily Pool - just to the north of the Lincoln Park Zoo. Just don't do it when a docent is giving a tour

www.explorechicago.org/city/en/things_see_do/attractions/park_district/alfred_caldwell_lily.html

If you don't mind the cost, you could always charter a sailboat (with captain) out of Belmont Harbor. chicagosailing.com

If you wanted to pick up a picnic basket for that romantic sailboat charter, the original location of Pastoral: Artisan Cheese, Bread & Wine is on N. Broadway, just south of Belmont. (Belmont Harbor being at Belmont, of course.) www.pastoralartisan.com

Sorry, I meant to give you an alternative, in case you didn't want to be on the north side (of Chicago).

If you were going to the Hyde Park neighborhood (Museum of Science & Industry; University of Chicago campus - including the Oriental Institute, Smart Museum of Art, etc.; Frank Lloyd Wright tour - studio, Robie House, etc.), then I'd suggest the Osaka Japanese Garden in Jackson Park.

How to get there: At the Henry Crown Space Center entrance of the Museum of Science and Industry (if leaving, you turn to your right - to your left, if entering), follow the sidewalk. Go over the Clarence Darrow Bridge (a lovely spot to view the MSI, BTW). You'll see the signs for the garden to your left once you cross the bridge.

Thank you all for the help! I ended up proposing close to home and she said yes! We went to Chicago and had a blast to celebrate. We visited most of the places you all suggested and had such a great time we can't wait to go back. Thanks again!

P.s. Have any honeymoon ideas?

Congratulations! Where and when are you getting married?
Depending on the season, I would look for a place farther south for the honeymoon. If you really wanted to start in Chicago, spend the day (or 2) and then get on the City of New Orleans train at 8PM. You get to Memphis early in the morning.
The Peabody in Memphis is top notch. After a day (or 2) continue south on the CONO to New Orleans.
Depending on where you live, you can fly home from NO.
You can delay the honeymoon. Our DD got married Memorial Day weekend in Baltimore. They just got back from their Hawaii honeymoon last week.

Thanks Tom! We're actually looking in south America. Costa Rica is in the lead right now. I'm headed to New Orleans next week for work and will add a little play in as well!