Heirs to the Lost World
There are nine levels of the Underworld reaching downward from the physical surface world. The first level of the Underworld partly overlaps the physical world and can be reached through the pits of caves. Deeper levels contain fierce rapids, thorny spines, rivers of blood or pus, fire pits, obsidian-bladed winds, etc. The deepest level of the Underworld is inhabited by the most powerful evil gods and spirits, etc.
Gates are the boundaries between the Underworld and the surface world or between levels of the Underworld. Gates are normally found deep in the depths of caves. There is no sharp boundary between the surface world and the Underworld. Gates are actually a smooth transition, but notable for two reasons: the geography of the Underworld does not correspond to the surface world and because some gates only work one direction. The surface world does not directly correspond to the Underworld. For example, two gates that are ten miles apart in the Underworld might be 1000 miles apart on the surface. Most gates are two-way, but not all of them. In other words, a gate that leads into the Underworld from a surface cave might only go into the Underworld, and if the traveler tries to retrace his steps, he will not find himself back in the cave on the surface but rather deeper in the Underworld.
Exploration in the Underworld is incredibly difficult for many reasons. The most obvious reasons are those common to travel in all caves: the darkness, lack of stars or other landmarks, the three dimensional nature, etc. The one-way gates and lack of correspondence with the surface is another complication. In addition, tunnels and caves in the Underworld can slowly shift after years, making old maps of any area mostly worthless.
Finally, and perhaps most importantly, the Underworld has a corrupting effect on all who enter it due to fear. The incredible fear caused by the Underworld can cause loss of Tonalli which can lead to the complete loss of this part of the soul and becoming fear-cursed. Magic can be very powerful in the Underworld, drawing power form the character’s own fear.
The region of the Underworld that is connected with caves found mostly in the southern Yucatan lowlands and Guatemalan highlands is known as Xibalba. This region is populated by fear-cursed humanoid known simply as Xibalbans.
The city of Zuyua is the only known city in Xibalba. Xibalban emissaries from this city taught the Mayan Caterpillar Lords secret codes to aid them in their Underworld travels. These codes were passed down through the generations and became known as the Language of Zuyua.