decompilers

does anyone know where i can get one so i can start trying to do edits, or is there some other way of doing it?

man i found the tool winbsp which uncompiles bsp files but, when i try to decompile some esf maps it crashes. im not trying to steal ppls work, i just want to edit the map so its better like wu_spacearena, i want to make the hallways bigger and the top walls a solid. can someone...