7. There are Trap Doors in Bryant Park
In Bryant Park, there is a not-so-secret trap door that leads to an underground power vault. The power generated in this room is used to power the Winter Village and Le Carrousel. You can spot the outline of the trap door by looking for pavers that are surrounded by metal.
Another trap door is hidden by a plaque that commemorates the efforts of various people and organizations involved in the park restoration from 1980 to 1992. What this plaque conceals is an escape hatch for the library stacks beneath the park. This door provides is a second point of exit for employees working in the stacks below, besides the exit which connects the subterranean space with the library above.