Hush's Hideout

Hush owned and maintained a hideout in Park Row which was located in the mega-prison of Arkham City.

Arkham City Incident
Hush retreated to this hideout after regaining consciousness in the Church (he was sedated by a doctor when he had cut off his face), where he worked on the final parts of his elaborate plan to take revenge on Bruce Wayne. He set out to kill three more people (the other three he had murdered before his transfer to Arkham City), and then made a mask that looked exactly like Bruce Wayne's face. When Batman, who was tracking down the murderer of those six people, found Hush's hideout, he was locked inside by Hush, who then finally took off his bandages and revealed his new "face", before leaving Batman behind inside his hideout.

References to Scarecrow

 * You can find a Fear Gas canister in the room.
 * The way the mirror is shattered slightly resembles Scarecrow's mask.

The following things are not a direct reference to Scarecrow, but they might have a connection to him:
 * The Mirror on the wall of the Hideout appears to not reflect Batman and the gate that locked Batman in is still reflected even after Batman unlocks it.
 * If you listen closely when standing in the room, you can hear eerie whispering.

These two factors might hint at the room actually being filled with a small dose of Fear Gas, though not enough to have a great effect on anyone in there. There appears to be just enough to make the room scary, without driving anyone insane.

Trivia

 * There is a resused texture from Batman: Arkham Asylum on the wall, the sign Frank Boles was holding when he died saying, "Dead End."
 * There is a gramophone in the room that plays an eeirly version of the lullaby, "Hush, Little Baby." The lullaby mentions the mockingbird, which is also the password to unlock the door to leave his hideout.