From Istaria Lexica
There doesn't seem to be any official resource to the mod. Be aware that the downloadable file is packaged wrong. The below description shows how to handle everything correctly.
- Close your istaria client
- Open your istaria folder
- On 64-bit systems (en), defaults to: C:\Program Files (x86)\istaria
- On 32-bit systems (en), defaults to: C:\Program Files\istaria
- Create directory resources_override (may already exist)
- Enter directory and create sub-directory textures_agh
- Enter directory and create sub-directory terrain
- unpack the downloaded rar file
- Enter unpacked directory \resources\terrain and copy all of it's content into <your_istaria_directory>\textures_agh\terrain\
- start your istaria client
- hope it works :)
Incase you have troubles to get it running you may find help by asking other players on the istaria community boards.