How the **** has this shit been hiding from me? This shit is awesome.
Basically, everything is made of blocks you can destroy and build. You can make houses, dig under ground and find gigantic alcoves to explore. It's just so much ****ing fun. I was building a vault like thing and found a huge cavern and after some exploring found some water, I swam around and found a good air bubble, I built a house, expanded on it but got flooded in, swam out back to daylight and I'm now building a huge tree house.
GOD DAMN THIS IS AWESOME
http://minecraft.net/play.jsp
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