Decorate T-shirts. You’ll need two plain white 50/50 polyester-cotton tees, fabric paint, brushes, and shake-on glitter, rhinestones, buttons, or other embellishments.
Teach your grandchild a hobby you love: crocheting, guitar, woodworking, cooking, etc.
Go swimming in a body of water that your grandchild has never experienced. Usually do the pool? Try a lake.
Take photos of each other posing at local landmarks and even just places you like.
Build an outdoor tepee from old sheets and a few poles.
Go to a museum exhibit you've never seen. The more unknown to both of you, the better.
Take a walk around your neighborhood, picking up interesting stones and leaves as you go. Then make a natural sculpture in the backyard. If you don't have a backyard, make the sculpture in a park's grassy area.
Tour your local firehouse. Call ahead to make arrangements; ask if your grandchild will be allowed to climb on a fire truck or sit inside and steer.
Collect seashells at the beach. Later, paint them using watercolors and give them out as favors at the next family dinner.
Pluck a thin, flat blade of grass. Stick one end between the tips of your thumbs and the other between your thumb heels. Straighten your thumbs out gradually until the grass is taut, pucker up and blow so that the air makes the grass vibrate, producing that high-pitched, piercing whistle. If that doesn't work, try two blades.
Name the constellations visible in the night sky or look up and view the next lunar eclipse or meteorite shower. For extra points, borrow a reference book from your local library to guide you along.
Get the schedule for local outdoor concerts and theatre and bring the grandchildren. Shakespeare in the Park not your speed? The Boss is on tour, too!
Go bowling. If you don’t have a bowling alley near your home, set one up in your backyard, using household items — such as empty soda cans and thin paperbacks — that you can easily knock over with an inflatable ball.
Collect fireflies in a jar.
Play make-believe — a young grandchild can be the mommy or daddy and you are the baby. Let her or him take care of you.
Browse a garage sale, giving your grandchild a few dollars to spend.
Get yourselves to a county fair and do as much as you can. Enter a pie-eating contest, strong-man challenge, and go on the bumper cars. Forget the cholesterol and don't forget the funnel cake.
Learn chess together. Once you get good, find a pickup game at the park but keep your hand on your wallet!
And speaking of pickup games, find one of any sport and join in.