Traps & Treachery is the definitive d20 System resource for traps, tricks, puzzles, and poisons. Traps & Treachery contains more than 60 complete descriptions of magic and mechanical traps, all beautifully illustrated, detailed guidelines on trap design and classification, comprehensive rules for creating and using poisons, new prestige classes, new skills, new feats, new equipment, new magic items, the Thievery clerical domain, and more.
This is a must have for any game master running a d20 system. I used it with Dungeons and Dragons 5e, and have found the chapters on traps and puzzles indispensable. The chapter on rethinking the rogue class with new feats is also quite helpful.
Now my traps have more purpose. The rogue, when looking for traps, will know why they recognize the trap--goblin creation, meant to slow down adventurers, meant to kill... makes the game more fun.