WinBSPC

Windows BSP Converter ("WinBSPC") is a utility used to recreate .map files for Goldsource BSP files.

Windows BSP Converter ("WinBSPC") is a utility used to recreate .map files for Goldsource BSP files. Results vary depending on the complexity of a given map.

To create an output file, WinBSPC converts the map into a single solid brush and carves out the geometry it finds in the BSP. The end result is a moderately acceptable brushwork, comparable to other decompilers such as BSP2MAP, with a comparison available below.

WinBSPC after opening

WinBSPC's attempt to decompile HL crossfire.

BSP2MAP's attempt to decompile HL crossfire.

Source: https://developer.valvesoftware.com/wiki/WinBSPC