I spent this weekend at a beach in Mantoloking. Riding the waves, sitting in the sun, and most importantly: building sand castles with my daughter. I’ve always enjoyed building sand castles, preferrably as the tide is coming in. You dig a trench, use that sand to build a horseshoe-shaped wall, and erect some towers behind it. Then, as the tide comes in you do everything you can to delay the inevitable. You’re about as likely to prevent the sand castle from being destroyed by surf as you are to prevent my daughter from having a tantrum when she’s skipped her nap, but sand castle building is decidedly the more pleasant of the two.

As I was kneeling in the sand, building my third epic sand castle in three days, turning my knees into hamburger, a thought came to me: Sand Castle Tower Defense would make a fantastic video game. It would require some fairly accurate water and sand physics. You could begin the game with only a cheapo shovel and plastic pail, and a single sea shell atop your lone tower. You’re given a single child and must assign him to build a wall around the tower and defend it from the incoming waves. As the game progresses, you earn better tools such as plastic cups to build extra towers, new seashells to place atop them, bigger shovels to dig deeper trenches, and more kids are drawn to your cause, giving you the means to multi-task and expand your sand castle domain. When the last seashell-bearing tower falls, your game is over and the kids go boogie boarding.