The 2*2 Target Block Door can be opened by striking the target blow with a bow.
In this guide, you will learn the method to make a 2*2 Target Block Door.
In order to make one, you have to place 12 pistons on the ground in the same way as shown in the following image.
Fill the space along the pistons by placing gray concrete blocks.
After this, you have to place three redstone repeaters on the back side and use redstone dust in the same way as shown in the image below. Add a redstone torch on the back side of the target block.
Now you can strike the target block with your bow to open up the gate.