Heaven Dust

After defeating the final boss and activating the self-destruct system, you will have three minutes to escape the mansion.
Instead of going to the garden at the bottom of the map like in the normal endings, you must instead go through the secret passage in Thomas's office, like described in his diary.
This "secret passage" refers to the metal door in the top right of his office, next to the chest.
You can open the first metal door by using the fingerprint copy on the console on the wall.
However, the second metal door to the end of the passage will not be opened until after activating the countdown.