This list is endless. Are they staying downtown or somewhere in the North Michigan Ave. area? North Michigan Ave. and Oak Street have the best shopping in a walkable area of any city I've been to. All the high-end names with boutiques along with Saks, Neiman Marcus, Bloomingdale's, and
Nordstrom and Macy's (to mention just a few: Chanel, LV, BV, Hermes,
Gucci, Ferragamo,
Prada, Tod's, Kate Spade, Loro Piana, Tiffany (and other luxury jewelers),
Coach, Barney's of NY, Disney Store for kids, Apple store for anyone, Niketown, Jimmy Choo; I can't list them all. Water Tower Place has Macy's, American Girl and lots of well-known shops.
Restaurants for any palate or ethnicity. Visitor favorites are The Cheesecake Factory, Ralph Lauren café near the Water Tower. A block off Michigan Ave is a favorite of mine--Pierro Gourmet, connected to the Peninsula Hotel but you enter from the street. It's sitdown or takeout--delicious!!
Museums: The Field Museum of Natural History, Shedd Aquarium are nearby down in the Loop area. The Art Institute (one of the very best collections of impressionists) is on Michigan Ave. near the lake in the Loop. It's a distance, but south of the main downtown is the Museum of Science and Industry-- a must for all ages--very interactive with new and old exhibits. I've been many times and see something new and visit old favorites each time. Great gift shop too.
The Lincoln Park Zoo is just north of downtown (about 1800 N.) and is free!
In the Loop is Millenium Park where the iconic city sculptures are. Everyone takes a pic of themselves near *the Bean* or the one with different faces and water coming out of the mouth. It's really cool, but hard to describe.
John Hancock Observatory in is the middle of North Michigan Ave. The Willis Tower (formerly Sears Tower) is the tallest building in the city and also has an observatory.
That's just off the top of my head. At least it's a start!