This is a very comprehensive and accurate texture pack, containing a large amount of incredible high-quality textures, ammo and weapon models (including Luma, Offset and Gloss textures). All of these, combined with DarkPlaces with its Offset Mapping support, provide an unbelievable effect and really dark atmosphere for Quake 1.
Seems like there is no need in "Ultra" pack, which takes 2.7GB of disk space,buthas only slight differences in quality.
Download 'rygel-dp-texturepack-high.pk3' and place it to 'ID1' folder in original Quake directory ('e:\games\Quake\ID1' in my case).
Open 'config.cfg' in the same folder and add the following lines to the end of the configuration file as shown on screenshot: r_glsl 1 r_glsl_offsetmapping 1 r_glsl_offsetmapping_scale 0.05