In my personal world, I decided to build an underground garden in a cave with a glass roof.
There's also a small farm and a house in an adjacent smaller cave.
The main cave was carved using TNT and enlarged using pickaxes. Everything was done in a legitimate way.

I intend to do the same in a snowy biome. You can already visit the location by going through the Nether portal and following the cobblestone path I have laid out.

Texture pack used: Sphax PureBDCraft 64x

Additional Notes

I downloaded the "I'm a legend" world from my cousin GTHGabriel before he built his great house and took on from there for my own project. That means the world seed is the same.

Go see what he did, looks awesome!
http://www.planetminecraft.com/project/im-a-legend-world/