This is a 3x3 piston door that is flush with the wall, but you can seen the pistons and observers on the inside of the door when it is opened. I did design a downwards double piston extender for it, because i couldn't find one online. (feel free to use the extender whenever you want) Further more, yes i know it probably isn't the most compact design out there but I really like it.

Some of the finer details:
1. It is VERY pulse sensitive!!!! so it can only be activated with a stone button, otherwise the double piston extenders will break.
2. The dimensions are: 15 blocks across, 8 blocks deep and 19 blocks high.
3. I didn't count the yellow lines in the dimensions, because they can, and probably will, be rerouted for personal needs.

Feel free to use it whenever you like it!
Hope you enjoy it, and if you really like it, don't be shy to give it a diamond!

~EndPlayz