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Update 16.11.13: Made a video tour! It was about time...

What is this thing?
The basic idea for this actually comes from something I made out of boredom during the summer. I really wanted to make a new map when 1.3 came out and this time I wanted to actually try to spend time on making a good-looking base, as my previous world was an ugly and terrifying mess of chests, TNT/creeper holes, half-finished buildings and (mostly failed) experiments. I really wanted to make an underground base for many reasons, so I started looking up nice seeds but couldn't find anything really suitable so I went to try seeds myself.

Now comes the weird bit, it took me exactly 1 try to find something good as I simply put in my favorite sentence and now I have all my favorite biomes, structures and everything you need within a stone's throw from spawn. Kinda hard to explain but this...

So I set up a quick base in the entrance of what turned out to be the biggest cave I've ever seen and started gathering resources, setting up basic stuff, and planning out my base. Eventually, I started building the base and some other things, and this is how it turned out.

The build
The entrance is on the edge of an island in an ocean, there's a Minecart system leading to it (and to other nearby places). I built it here because I wanted to build a sky mob trap as nearby as possible, and this place was almost ideal for it as I only had to lit up the island (and a few other very small islands around it) in order to get max rates for it. Almost everything was dug by hand, I had very little gunpowder for TNT. The digging actually didn't take that long. I started with the entrance area, then did the main room, the bottom floor and eventually the other rooms.

Everything is collected and build legit, survival mode, hard difficulty.