Therion is very powerful and flexible tool that allows to create and manage cave maps. It is also open to extensins to adapt it to particular needs. This is the advantage of the Open Source, and a modular design of the code.

This chapter describes how to extend therion

• localizing therion (and xtherion) to your language;
• inserting MetaPost and/or TeX code snippets;
• font specifications;
• creating new symbols;
• using "external" editors.