Observational Riddle. The game is afoot!
<< Check out this image for a fun example <<
This riddle makes you feel like Sherlock himself. How? It's elementary...
Observational riddles present you with a scenario (usually a murder, but not always). They include a list of details designed to distract you from the one, important detail that will solve the riddle. Usually, this detail will be an inconsistency, a lie, or a direct consequence of the solution.
To solve this riddle, you need to notice that small detail, and make a logical connection between that detail and the solution... basically, you need to play detective!
In order to work in an escape room, the answer to an observational riddle has to be a very specific word or phrase (this way, it can easily be used as a passcode). The details must also be crystal clear. If your players need to ask clarifying questions, then the riddle is too vague.
For the creative game master, observational riddles can be a fantastic tool to 'show, not tell'. Instead of writing the riddle, you can recreate the scenario with props and posters. This way, players can become detectives, and pick out the details themselves!