Mine is a pyramid (sorry for the not-so-great quality, I don't know how to screenshot on the 360) that I made with the help of a friend (he just cleared the sides). Inside there is an actual tomb, which I moved my AFK friend and locked him in there
Mine is a Large castle wall around a small village i'm building up. I did the wall alone and the village was a group effort with the people who joined me. (No photos or video of it yet until I set up my capture card again.)
To take a screenshot, you press the start button & press Y. Then follow the on-screen instructions to upload the photo to your Facebook account.