Reminds me of second grade... Using the massive amounts of blocks that all the kindergarten through 4th grade classes had, me and my friend built a castle. It started out as just a huge long wall one day when we had to do indoor recess because of rain. One day turned into two... three.. a week.. two weeks.
When we finished, what we had was the walls of our very own keep. Almost four foot tall, and big enough for four kids to sit in comfortably, and, a door for us to crawl in and out of, and ramparts and a tower to complete the look.
The best part? Getting to completely demolish it when the rainy days were over (^_^)