Hidden Achievement Guide

Simply dig down till you hit bedrock. You'll know when you reach the bottom by the tan and blue looking floor. It will also make a distinct sound when you hit it like when you hit land claimed territory.

The easiest method to do this is with an auger and just keep it aimed straight down. Also bring plenty of wood for frames or ladders to get yourself back out.

For this achievement you will need the .44 Magnum and enough magnum rounds to kill 44 zombies. It's pretty easy to get if you take your time and aim for the head.
I'm not sure if dogs, wasps, or the zombie bears count towards this achievement.

Most people probably get this one by accident... all you need to do is break your leg. A sprain will not do as it must be broken. If you sprain your leg, falling again should break it and grant you the achievement.

Similar to the Dig Deep achievement, for this one all you need to do is reach the top of the game world. There is an invisible ceiling that you can get to where you can't build or place any blocks to get higher. Once you reach this point the achievement should unlock.

The easiest way to do this is bring a stack of about 200-300 wood frames. How many you actually need will depend on your altitude when you start. Place a wood frame on the ground, jump on top of it and then keep jumping straight up while placing more frames below you. You'll keep going way up into the air (check out the view with the new distant terrain) and eventually unlock the achievement.

Make sure there are no zombies around when you do this. If they break a block while you are way up in the air you will fall and possibly die.

This is probably the trickiest of the hidden achievements but not that hard. What you need to do is get your temperature down to 0 while you are totally naked and 100% wet.

The easiest way to do this is find a snow biome that has a high elevation. The higher your altitude the colder it gets. Find a body of water that is deep enough for you to fully submerge in. Then strip down of all clothing, sit in the water and wait for your temperature to drop. To speed up this process you can wear clothing with a negative thermal value and drink either red tea or Yucca juice as both will help lower your temperature.

Getting your temperature down this low is dangerous and could result in death, be prepared to put warm clothing on and sit next to a fire as soon as you get the achievement.