Fabel Ich beschwere mich Konzern dnd riddles and puzzles Mentor Salon Analyse
A few challenging, ready-made riddle/puzzles (mostly door locks) : r/DnDBehindTheScreen
D&D - Puzzles - Cephalofair
The Game Master's Book of Traps, Puzzles and Dungeons: A punishing collection of bone-crunching contraptions, brain-teasing riddles and ... RPG adventures (The Game Master Series): Ashworth, Jeff, Hilton, Kyle, Bhullar, Jasmine, Three