Single player anyone?

Does anyone have a single player world? If so here is what you can post, this could help others on ideas for their single player world!
What have you built in it? Was it in creative/survival.
How long can you survive alone?
What are the best farming methods?
All these are great to ensure everyone gets a good go at single player fighting off the mobs before PvPing because as you all know, Minecraft Factions server is a great way to PvP, but maybe stick to mobs some of you
Don't forget to post, it could help someone in single player OR any multilayer server.

What have you built in it? Was it in creative/survival.
I build a roller-coaster, but it failed as if you rode it in survival you burnt to death, but was built in creative.
How long can you survive alone?
I have not counted track on my single player world, but it must be a very long time, at the start it's very hard, but gradually gets easier.
What are the best farming methods?
I do like this; I have never grasped the design on a multiplayer/survival server/mode, but I attempted it once on Minecraft Factions.