I've completed the Castle of Zombies (several times), done all the boss ciphers, beat the training robot (several times), and dug to the Old Machine that needs a lava bucket. I also have Diamond Sword, Helmet, and Boots (working on Diamond Chestplate and Pants).
Where can I go from here? What lies beyond the Castle of Zombies and how do I get there?
Here is my map, currently: