Wall mounted ball run. This would be great for kids who are too young for the marble runs. Could be used as a music installation if there are movable obstructions in the pipe that make sound when a ball touches them
Colorful Fizzy Fun: Pinner says "This kept my 2 year busy for an entire hour and my 4 year old busy for 2 hours! Drop vinegar tinted with food coloring onto a pan filled with baking soda. Sheer minutes of colorful fizzy fun!