Litterally last day submission lol. I have two practical redstone contraptions for you guys. Both are in my base right now! While I understand that the limit is 1 contraption I did not feel right leaving one or the other out. If I had to pick one out of the two featured in this post, it would be the Elevator since its a more advanced use of redstone mechanics and flying machine technology. HOWEVER, to those judging, feel free to pick the one yall like the most! 
IGN: Zalkruel (1 underscore on each end, forums doesnt render it well :(
Coordinates: X:691 Y:79 Z:-5076 (for door), X:622 Y: 79 Z:-5075 (for elevator)
Brief Description: Two practical-but-satisfying Builds for your viewing pleasure. 
The first two screenshots is the concealed 6x6 flying machine piston stickyblock door (sorry for the long name, I suck at names).
The next Three screenshots will focus on the base’s E L E V A T O R.
You read that right. An actual 4x4 elevator made from the same flying machine technology that made the giant hidden door. You may need to enter spectator mode to examine the full mechanism. Access tunnels have been created to allow judges to see most of the circuitry.
Obligatory Favorite TV cowboy: Rango (Since it is the only correct answer.)
Thanks for reading!