hours of time wasted here:
http://andyslife.org/games/sand.php
I like to make mazes of c4 that create bubbles in which i can place lots of nitro and gunpowder and then make a big wax ball and put some torch in the middle then when the flaming wax finally melts enough to strike the c4, everything goes up in a spectacular finale! (nitro is key) you can turn off the stuff from above by clicking the numbers next to those names on the bottom right till they say 0. enjoy.