Creative Mode - pointless, pretty much a waste of time
Those huge and amazing constructions you see are often not made in creative mode (you must be mad to do something like that), maybe a few touches here and there, but mostly there's another mod or program involved, like MC-Edit for example.
And yes, creative mode is a good way to try out your ideas before going into survival and building them. However, you'll soon find out that it's best to have a somewhat not established plan, adapt to your surroundings and experiment while you're vulnerable on creepers, redstone traps and whatever you wish. Because otherwise the game becomes predictable and you're most likely get bored of it sooner than you should.
Once I made a really cool castle surrounded by lava and everything in creative, then I switched the world to survival by putting it in a server so that I can play on it with my brother and my cousin. At first it was nice to play in an awesome medieval castle, but there wasn't anything else to do… Monsters couldn't handle the defenses and we were clad in fully enchanted diamond armor, swinging diamond swords and shooting power 5 enchanted bows. It got boring really quick and we ended up destroying the castle ourselves. Survival worlds last much much longer…
See my point?
Something similar happened to me once: I had this really neat house in a savanna and I had been playing on that map for quite a while… I was at the stage of gathering diamonds for a full armor. Then, one day, my horse fell in one of the pretty shallow crevasses near my house and right there, so close to the surface, was one of those big old libraries that you find in dungeons. Basically, an End Portal right under my nose this whole time!
