Misspellings
Hopefully, as you create notes and other material for your escape room, you are doing some proofreading to ensure that the language is correct. But, sometimes you can intentionally introduce mistakes to highlight words that add up to a secret message. One simple such mistake is a misspelling of a word.
As I awoke, there appeared before me a body of pure light. “Loook upon me,” it said, “and hear my words.”
“What do you want?” I stammered
“You have been selected for a quest,” it said. “You must travel over the highest mountains and undr the thickest forest canopies. Go to the temple of peace and find the chairrs of the five kingdoms.”
Look closely at this note and you will see that there are exactly 3 misspelled words: loook undr chairrs (look under chairs), which gives a clue on where to find an important item.
Make sure that your misspellings are egregious (that is, easy to spot) but also unmistakable for the word they are supposed to represent. Players need to be able to pick out the words but still be able to understand them. Keep in mind the reading level of players. Young children or English-as-a-second-language players are likely to have more trouble with a puzzle like this.