Hi! This post will show you how to make a classic Jeb door in Minecraft. Jeb is the developer of Minecraft and as far as I know, he found the design online when pistons first went live in-game. It is not too resource-intensive so it is fairly feasible, even in Survival mode. Also, this tutorial assumes you have basic knowledge of game-play and possibly basic redstone mechanics.
The Jeb door is a secret piston door. When properly built and covered it is extremely difficult to find.