Personally, I love downtown Chicago. Staying in a place like the Palmer House, which boasts one of the loveliest lobbies or the Drake hotel is another wonderful place with a great lobby. Even having lunch somewhere and hanging out in these lobbies and listening to someone playing the piano is a lovely way to spend some time. Depending on when you are going, many of the Chicago Hotels offer special discounts and packages. Staying closer to Navy pier is a wonderful option too. Many lovely eateries.
Waking up and walking along the lakefront in the morning or taking a stroll along Michigan avenue and window shopping (and people watching) is very fun!
Even if you only want to make a day of it, take the Metra train, from Richton Park and it will end at Millennium Station which is right by Millennium Park - (sorry...you may know this already.) You can have an inexpensive afternoon, having a picnic lunch in the park (try to check and see if there is any free entertainment going on at the band shell there) or take in a matinee Broadway show. The theatres are very near the train station - easy walking distance.
Love the city! Happy Anniversary, whatever you choose to do.
With a household like that....are you SURE you can't get away for longer????? Wow!