The Works- http://www.attheworks.org/
This is similar to Cosi but on a much smaller scale. The cool thing about The Works is that a family membership is only $60. With this membership you are able to get into Cosi and thousands of other science museums around the country and several other countries. We have used it for ones in Cleveland, Nashville, Dayton and Helena, Montana. We have paid for the membership several times over with getting in free at all the different museums.
Columbus Metro Library-
The downtown branch has several great activities through the summer.
Alum Creek State Park
Many great areas to go exploring, fishing, boat rentals and the beach. I have found that this beach gets a little crowded for us, but we have usually been there on the weekend. It may not be bad during the week.
Columbus Museum of Art -
Admission is free on Thursdays.
Discover Ohio- http://www.discoverohio.com/
The website is filled with lots to things to do. For instance I found that this weekend in Cincinnati there is an exhibit on butterflies of Japan down in Cincinnati. They will also send you a free packet with tons of info and maps.
Rising Park -Lancaster, OH
We go here often. My parents moved down here about 2 years ago. The city has completely redone the playground and it is wonderful and picnic areas. My boys could play here for hours. There is also a pond for fishing, tennis courts, basketball, and horse shoes. And don't forget about the hike to the top of Mount Pleasant. Just a word of advice. This hike is really steep and there are very limited hand rails when you get to the top. So please watch your children very closely.
Thanks to CMOTC mom Mahala for sharing these fun summertime activities with us!