If you're in Bloomington for the summer, or even at the beginning or end of the school year, there are a million different things you can do in the hot weather. I'm just going to give you one example of a really fun, inexpensive activity you can do close to IU: canoeing at Griffy Lake.
Canoeing at Griffy is cheap and really fun! I went a few weeks ago during a summer visit to Bloomington. It's only a maximum of ten minutes away from campus, and it's a blast! It was my first time canoeing, and I absolutely loved it. Each canoe can fit up to 3 people and is only $7 an hour (so split between 3 people, that's only $2.33 each!). There are also hiking trails, and neither entering the area or parking costs anything extra.
For more technical information, check out the official page for Griffy Lake Nature Preserve here, and for other Bloomington activities check out the links below: