thanks for the answers
I don't know what Metapost or CSS box-shadow are (yet...)
MetaPost is the programming language used to describe every symbol and line that Therion draws. In your "layout"-"endlayout" section of your configuration, you add a "code metapost" and "endcode" section, then you add the code needed to redefine the cave walls that you are using. It's complicated, since it is a programming language. Takes some practice. https://therion.speleo.sk/downloads/thbook.pdf - look for the "New map symbols" section, which shows some examples. Loads more examples: https://therion.speleo.sk/wiki/metapost And if you want to see all the MetaPost code that Therion uses by default, see: https://therion.speleo.sk/wiki/metapost#how_to_get_therions_metapost_code_an... This is where Martin was suggesting you look for the line that looks like this: def l_wall_pit_AUT (expr P) = I'm still in the process of learning the language myself, and am not yet good enough to write what you need.