This is really cool because not many people would jump into lava on purpose. Hope you enjoy.
What you need is
4 buckets of lava
4 buckets of water
First dig at least 7 blocks down then at the bottom two blocks make a little room you can make it deeper if you need it to be.
Now play sign on the 2nd block from the top and then place your next to sign on both signs you just placed. Then place signs two blocks under the sign. The same way.
Now go to the top and place lava over the first four signs. And then go down under the lava and on the other four signs place your 4 buckets of water.
Now while you are in the room you made under it stick to the side as many blocks as you want making a passageway and take straight up once you get how many blocks you choose place ladders to go up and instead of a ladder on the top lock place a block matching the surrounding blocks. In my case it was sand.
now you are done you can tweak it or change it however you want and make it bigger or smaller. To go in just jump in the lava and it will only take away about 1 heart because you will quickly fall into the water and be saved. I hope you enjoyed this instructable. Don't forget to vote.