It works fine, pull the lever and the pistons pull the blocks back. Moving forward, however, I would like to somehow implement a way for me to close the hidden door behind me, ideally working so that I could also open them from the inside for maximum stealth. Here is a shot of the (simple) circuitry:
You can use a button or pressure plate to send a pulse of power, rather than a lever that will stay on once flipped.
Walk in when the door is open and it will close behind you. You can use repeaters to adjust pulse length and delay. Put a similar button on the inside for exiting. A bonus of this is that a stone button placed on a stone block blends in well.
For a more advanced solution, you can make a flat wall on the front and use two sets of pistons instead of one. The first set will pull the blocks into your base, and the second set will pull them to the side. This requires more careful timing and more room for repeaters and pistons on the inside. If you use an RS-NOR latch, you can make the door stay open until you enter and step on a pressure plate.
I recommend a T Flip Flop. Google it, there are several possible circuits, most are simple to construct. This allows buttons to toggle the circuit on and then off. I use two buttons, one on the outside hidden, and one on this inside hallway. This allows you to open the door, enter your place, and push the button to close the door. Then to exit you push the same inside button to open the door, exit, and push the outside button to close the door.
For a really fancy entrance lock method, I use a BUD circuit to sense a block of grass. When you use a hoe to convert the grass to farmland, the door opens. Then a few minutes later the farmland converts back to grass and the door closes. No visible button or anything and you need a "key"(hoe) to get in.
I have 3 different answers. One is low tech, the other two are a bit more complicated.
1.) The low tech solution. Use a redstone torch as a not gate to power the pistons normally. A wooden button can be shot with a bow and arrow which causes the button to remain depressed until the arrow despawns(one minute). You can have more then one button to power not gate so inside and outside buttons are possible.
2.) A pulse length control. You send a redstone signal to this device and it outputs a pulse with a controlled length. (Also called a pulse extender if you want to search internet for other examples) In your case, a button would be pressed and the door would stay open for an adjustable amount of time.
It consists of 2 hoppers, pointed at each other. You send a signal into a piston which pushes the redstone block to the other hopper. This causes items to begin to transfer into that hopper. A comparator reads that hopper and when it fills enough, the redstone block is pressed back to it's original location.
One hopper is filled completely with stacks of items. I use cobblestone. Dropper labeled delay control in photo is filled more or less to control output pulse length. I put two stacks in it for a pulse beyond 30 seconds. Play will fill level of this dropper to get the desired pulse length. (How long you want door open)
You will see the redstone labeled output to doors is in the other redstone block position on the photo on the right. This is useful if you need to power something for that length of time, in your case, you need to no power pistons for that length of time so the photo on the right is the proper position.
3.) The T flip-flop. The T stands for toggle. What this means is that you can toggle the output using power from any source. Press a button and the door opens, press it again and it closes. You could have a button hidden outside and a pressure plate inside. This would cause the door to self close and self open from the inside.
A simple flip-flop requires 2 repeaters, 2 sticky pistons, and a redstone block. It uses a game mechanic where a sticky piston powered for 1 tick will push a block and not pull it back. When powered a second time, it pulls the block back. The image shows 3 images, the bottom 2 are the machine in two different states. One would power the door, one would not.
As a previous answer stated, there are several variations of the T flip-flop. Another one that I use requires droppers, a hopper, a comparator and a couple repeaters. I will demonstrate it incase you can't get slime balls.
The arrows indicate the direction the droppers face. The hopper points at lower dropper. Put only one item in one of the droppers. It works by powering the top dropper. This causes the item to cycle through them. We read the bottom dropper with a comparator. It will have the item every other button press. It toggles on, and then off. Just as the previous example does.
I just built a little example setup for you. My example includes a solution with pressure plates to control the sticky pistons. Please see the following printscreens:
This shows a basic setup to build a door with sticky pistons.
This is a very basic setup to build doors with sticky pistons. In this example, use redstone torch to invert redstone signal. This makes the pistons push the wood blocks together. As soon as you step on the pressure plates, the redstone signal gets cut and the pistons will open the way. The pressure plates also have a little delay, so you can pass easily.
Of course you can also use a button which also brings a little delay with it. If you need more time add some redstone repeaters to your circuit.
I hope this gives you some inspiration! Greets
Use a redstone repeater, if you are low on space. Once you place one, right click on it up to three times to increase the delay time.