Someone requested I show off a piston door, so I decided to show off a hidden door that's fairly simply to make.
I think I included everything in the video but I'm uploading the test world just in case because redstone can be confusing to explain.
World Download: http://adf.ly/726741/hiddenpistondoorexample
* I think I mentioned it in the video, but if you guys want a tutorial on how to make your own flatgrass I can do that, its a very useful thing to have.