Big Mountain Overlook near Cowans Gap State Park, Pennsylvania
Learn to cook/bake - use measuring spoons, cup, etc. - builds math skills!
Build a bird house.
Paint rocks.
Discover lost toys under your bed and in your closet
Take a hike at a park (Double Rock, Gunpowder Falls, Oregon Ridge, NCR Trail, Loch Raven, etc.).
Ride your bike, scooter, or skateboard.
Rollerskate.
Make a fort with a blanket or several boxes.
Build a marble track/roller coaster out of pool noodles, empty toilet or paper towel rolls, rolled up paper, etc.
Build an obstacle course in your yard with pool noodles, boxes, etc.
Make your own Skee-Ball game: Frugal Fun - website has many more activities to do
Play a board game.
Build a puzzle.
Read a book.
Create your own comic book.