Go on a hike. - Hiking can be a great way to chill out by the water and also get a good exercise in on those hot days.
Go for a walk. - Going for a walk can be a great way to relax those hot muscles.
Learn a second language. - Stay inside and learn another language!
Do a puzzle. - Puzzles are a great way to keep your hot mind busy.
Read EVERYTHING. - Any book lovers out there?? Start picking up some good reads! So many books, so little time!
Yoga. - Yoga is a great low-impact way to get your juices flowing and keep your mind off the heat.