In this box there is one sonar sensor that you need to keep the correct distance to in order to go to the next level, i liked this since I wanted to make the puzzle physical and interactive. in my game I mounted two sonar sensor on the top together with two large RGB Leds  to get visual feedback. When you start the game they are both red and if you start playing around you'll soon enough hold your hand at the right height over one of then and they'll become green - but only as long as you keep your hand there. Now the player should realize this and hold their other hand above the other sensor and when they are both green they will flash blue and you are done with level 1.