This is Therion, cave surveying software. It produces complete, always up-to-date cave maps. The map is automatically updated after loop closure, blunder fix or map symbol set change. It's particularly well suitable for documenting large and complicated cave systems. Therion creates realistic 3D models from 2D maps without quantity of additional information. LRUD dimensions are also supported. Documentation is in the Therion Book (file thbook.pdf), which can either be downloaded from https://therion.speleo.sk/downloads/thbook.pdf or compiled in the `thbook' directory using pdfTeX. Installation (compilation) is described in the Appendix of the Therion Book. There is also much excellent documentation contributed by users on the wiki at: https://therion.speleo.sk/wiki/doku.php Web page: https://therion.speleo.sk Copyright (c) 1999–2021 Stacho Mudrak, Martin Budaj Distributed free under the GNU General Public License