What's your favorite Enigma / Riddle / Sentence Puzzle?

Tomorrow is a big event at my university. I'd like to make a fun thing where the people of the Board Game society I am in can try to find me for a riddle, kind of a Where is Waldo in a place where there is a crap tone of people to find the NPC that'll give them a Riddle (Maybe something to win? No idea how I could do that...