Unleash your inner child with Minecraft, a free block based sandbox game.

If you're looking for a free sandbox game with unlimited possibilities Minecraft is hard to beat.

It's a Java based sandbox game in which players place blocks, fight monsters, construct massive pieces of art & architecture and all for the sake of that butterfly stomach feeling  at the end of it all.

Basically, you're only limited to your imagination, there is a wide variety of public and private servers on minecraft and thankfully you can play it anywhere as it is java based (assuming you have java installed, but mind you java is even more commonly found then flash now a days). It's an awesome experience from start to finish and it's more then easy to let the hours pass when you take the time to play, you'll quickly find yourself in a vegetative state; focusing purely on constructing the last half of your missile silo base or building a gigantic underground fortress, the potential is literally endless & the developer makes a great deal of effort to keep the community happy. This game is definitely getting a big fat steam of approval from the wizard, as it's hard to beat in terms of creativity.