Tutorials/Secret door

Using Lava
The most simple way to build a secret door is to use Lava. You have to build a frame, place ladders next to it (to stop the lava) and place some rails with a minecart behind it. Then you're done.

Here's a video tutorial of building that type of secret door.

Secret Painting Door
start by making a 1x2 gap where you want your doorway to be and placing signs down the sides of it. Then you place paintings on the bottom sign untill it fits