My friends and I simply like doing little tournaments when we get together.
We each take like an hour or so, and build a maze for the other one to solve.
Once, we had our friend visit from New Mexico, and we did a three player version. My maze a single hairpin turn that triggered a length of undergorund dynamite leading to another player's maze (annihilating it completely). I broke the world, but my friends response was priceless!
Me: Hey, I have to leave for work in a few minutes, do my maze first!
*He walks in, steps on the pressure plate, turns around and walks outside*
Him: "Dude your maze sucks, it doesn't work proper..."
*BOOM bang pow kachoo POOF*
*A line of smoke and crumbling earth leads to his maze*
*everyone gets kicked off the server*
*
*
We log back in and finds that his maze is left in shambles, stuff was floating around randomly, rooms were indistinguishable from each other.
Me: Well, I have to go to work. have fun guys!
That was the most memorable. That's always done in creative mode.
not in creative mode: I'm the pit-digger of my group. I dig down. I then use that to build a castle. My friends call me the wildman, I only come to town for food. Otherwise I live in the wilderness building big things. My favorite was a large catacombs.
I went to the tallest mountain near town, and killed myself and marked where the spot was. I dug straight down from there, and that was the entrance to the underground temple.
Then I built a temple as my way to get out. It was one of my favorite castles ever.