Marble Races with a cheap pool noodle (occupies the kids for hours.) Did this, but instead of cutting the pool noodle, the marble is small enough to fit inside the full noodle to roll down. Then can use the noodle for other things too!
One pinner suggested, "Use train tracks as marble tracks in the block center!" I was just wondering about my existing train table/tracks, and if they are still embraced in this approach our Board appears to be moving in.