One of the iconic puzzles in Act 2 involves a miniature train set. To solve this, you'll typically need to find several train cars and a specific power source or switch. The train cars are often scattered across different rooms, sometimes requiring you to jump across gaps or solve smaller environmental puzzles to reach them. Once you have all the train cars, place them onto the tracks. The order might matter, so experiment if the puzzle doesn't immediately activate.
The power source for the train is usually a lever or a button located in a control room overlooking the train set. You might need to power up a generator first, which could be in a separate, dark room. Once the train is running, it will often reveal a hidden passage, drop a key, or open a previously inaccessible door. This puzzle requires patience and careful observation of the environment for clues. The Neighbor will often patrol this area, so be prepared to hide or distract him.