The Amazing Falling Sand game (chir.ag/stuff/sand/) is so much more addictive than you may think at a first glance.

We won’t spoil your fun by giving you too much detail on how to play this simple interactive game. Just use your mouse and start ­drawing walls to ­observe what happens. You can change your ‘drawing tool’ with options at the bottom, and this is where the real fun starts. Do heed the addiction warning though: before you know it hours may have passed.