This is a trap for the mobs or enemies. If anybody opens the trapped chest box, he will fall straight into the lava.
In this guide, you will learn the method to make a Chest Trap.
First, you need to dig eight blocks of the ground and place sticky pistons in all of them.
After this, dig five more blocks of ground in front and add iron blocks in it.
Now you have to dig 5*2 blocks of the ground and theory depth should be two blocks. And then add lava buckets in it.
Place pistons and iron blocks on the opposite side in the same way as shown in the image below.
The next thing you need to do is to place two trapped chest box at the back and use redstone dust on the outer side of pistons.
Now you have to dig the ground at the back of trapped chest boxes and place four redstone repeaters in it as shown in the following image. Use redstone dust between these repeaters.
Add a redstone torch and one repeater on the both the sides and connect them using redstone dust.
The pistons will push the iron blocks forward to hide the lava.
If anybody opens the chest, he will fall straight into the lava. Finally, you have to cover the redstone by placing iron blocks on all the sides and at the top.