One room, several locks
The study belonged to someone who did not want visitors leaving. Every puzzle can be solved with what is in the room: numbers hidden in plain sight, an object that only makes sense next to another, a note that means more the second time you read it. No outside knowledge is needed.
Hints come in stages, from a gentle nudge to a clear answer, so you can choose how much help you want. Your progress is saved in your browser, and the game records your time and the number of hints used when you escape.