BSP2OBJ is a Python module and command-line utility that is capable of converting BSP map files into OBJ/MTL files (with accompanying PNG textures). It comes with support for Quake, Quake 2 and Half-Life maps.
The easiest way to install BSP2OBJ is to simply use pip like so:
pip install bsp2obj
The installation process should create an easily accessible bsp2obj command-line utility.
Both Quake and Quake 2 store map and other associated metadata within PAK files. As such, you'll need to let BSP2OBJ know the target PAK file with the -p argument. Additionally, you'll also need to pass along the path of the colour palette within the PAK file to ensure texture data is decoded correctly. This can be done using the -c argument.
Here's how to extract the starting level of Quake 1:
bsp2obj -g q1 -o q1_start -p Q1.PAK -m maps/start.bsp -c gfx/palette.lmp
And heres how you'd extra the first demo level from Quake 2:
bsp2obj -g q2 -o q2_demo1 -p Q2.PAK -m maps/demo1.bsp -c pics/colormap.pcx
Half-Life differed slightly from Quake and Quake 2 by ditching the use of PAK files and opting to instead store textures and other metadata in the file system. As a result, you can omit the -p argument in this case, and instead pass absolute paths to the required .bsp and .lmp palette files.
Here's how I went about extracting the first level of Half-Life from my Steam library on macOS:
bsp2obj -g hl1 -o hl_c1a0 -m /Users/measuredweighed/Library/Application\ Support/Steam/steamapps/common/Half-Life/valve/maps/c1a0.bsp -c /Users/measuredweighed/Library/Application\ Support/Steam/steamapps/common/Half-Life/valve/gfx/palette.lmp
You may provide the optional argument -e to export files contained within a PAK file that match a given regular expression. As an example, one could dump all of the .bsp files in a PAK file like so:
bsp2obj -g q2 -p Q2.PAK -e ".bsp"
Alternatively, if you provide a pattern of * every file will be exported:
bsp2obj -g q2 -p Q2.PAK -e "*"
If you'd prefer to list files within a PAK, swap the -e flag for -l