Base 101: Underground base

 So here we are, with the underground base finally. I took my time there because since I started a new world with the Mo's Creatures mod, I've been busy farming a lot (and for once I had a lot of luck finding diamonds, so I was able to make four quarrys now).

Anyway, I just made a small underground base between layers 12 and 22 (aproximately) and decided to show it to you all.

As you can see, it's quite high so the trees can grow. I prefer the white bark ones because they always grow four to six logs, meaning their top height is about 7-8, and don't have extra logs hidden between the leaves.
I put three trees here, separated 3 blocks from all the walls and between each other (2 blocks of separation between the tress would have been enough, but then the leaves blocks tend to merge, and we will get less saplings after cutting the tree).

Finally I made a small recess of three high and one depth, then excavated a 2 high and one depth additional one, added a line of dirt , water, covered the water, added some torches, and used a hoe to plant some wheat, then added two chests, a crafting table and two furnaces (you can't see them in the photos, I'm afraid), plus a bed in case I want to sleep.

So there  we are, a fully functional base underground. It only lacks animals, but the pain of taking dirt with grass all the way to the underground, with all the time it takes for animals to spawn once you are down there makes it for me something not to worth the effort.

Ok, so now with the pros and cons of an underground base:
Pros:
Self-sufficient: it's the only base with ready access to all the material needs you might have in Minecraft, given enough work to make room for the trees. Mi advise would be to chop the trees every time you go back to the base, and replant, no matter your needs of wood.
Mining-oriented: extremely easy access to mining.
Stealthy: it's underground, so it's unlikely other players will find it in SMP (saving glitchs).

Cons:
Effort-intensive: unlike a surface base, you will have to clear room in all directions so the trees will grown up. Also, you need to provide light.
Stealthy: you might have trouble being able to reach your base back unless the path is marked... in which case the base turns into one more easy to find in SMP by other players.
No sun: again, you will need to provide lightning to your plants, and more importantly if you play using Industrialcraft, you won't have access to solar light unless you make a solar generator in the surface with HV cables taking the power down there... which again will make the house easy to spot in SMP.

In case you want to look into more detail this kind of base, Paulosoaresjr has two or three videos showing how to setup underground farms in his "how to survive and thrive" video list.

Have fun!