Never build a dungeon you wouldn’t be happy to spend the night in yourself. The world would be a happier place if more people remembered that.

Terry Pratchett (1948-2015) English author
Guards! Guards! [Lord Vetinari] (1989)
    (Source)

Said while imprisoned in the dungeon. A few scenes later, he adds, to himself, Never build a dungeon you couldn’t get out of, while escaping.