A riddle that sticks with you might be: “I have cities, but no houses. I have mountains, but no trees. I have water, but no fish,” and the answer is a map. Other puzzles include “The more you take from me, the more I grow,” which is a hole, and “I speak without a mouth and hear without ears. I have no body, but I come alive with wind,” which is an echo. Some of the most unsettling are dark riddles like “What is red and bad for your teeth?” (a brick) or “What falls down but never breaks?” (nightfall).