Field Museum  (www.fieldmuseum.org)
The hours of operation is 9am -4pm, with the last admission at 4pm
Other FREE  days are the second Monday of every month. Parking is $15/day.
 

Adler Planetarium  (www.adlerplanetarium.org)
Check out their web site for exact hours and parking fees.
The museum is FREE on the following days:

Additional fees for shows applies

Museum of Science and Industry  (www.msichicago.org)
The hours of operation are Mon- Sat 9:30am-4pm and Sunday 11am-4pm
General public parking is $14
2008 FREE dates:


Shedd Aquarium
Check out the web site for exact hours of operation and parking rates.   
2008 discount days:
 
Additional fees for shows     

Day Frog (www.dayfrog.com)
"Multiple Mania" to Chicago!
http://www,dayfrog.com/pdf_forms/Muliples_Mania.pdf
Over the next year, multiples will be admitted for a day at a discounted price of 2 for 1 on the 22nd of every month. Day Frog is a 4000 square foot facility right off Michigan Ave. and is open 7 days a week and nearly all holiday. Each child must be accompanied and supervised by an adult.