This is probably the best way to hide a chest in minecraft.
Inside a wall!
Don't worry, no minecarts involved. :)
Step 1: Build It!
Just follow the pics...
You will need about
-about 42 wood (or building blocks)
-2 chests (if you want a double chest)
-2 wood slabs(or slabs of building blocks)
-2 wood stairs(or stairs of building blocks)
Step 2: So, How Does It Work?
Words to know:
The box that defines the shape of the block and how players/entities bump in to the block.
What happens is that when the two stairs(at the left) merge, the texture will change, however the white stairs will still have the same hitbox as when it was not merged. This means that at the corner of the white stairs there is a "hole" which allows you to open the chest behind it. And if you are wondering why there are upside down half slabs on top of the chest, it is because chests can't be opened if there is full/solid blocks above them.