Riddles in the Dark - Voiceless it cries, Wingless flutters...

Riddles in the Dark - Voiceless it cries, Wingless flutters... (59th Street station; downtown A, B, C & D trains)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (42nd Street station; uptown 1 2 & 3 trains)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (59th Street station; uptown 1 train)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (59th Street station; downtown A, B, C & D trains)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (Canal Street station; uptown N, Q & R trains)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (23rd Street station; uptown A, 1 trains)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (28th Street station; uptown N & R trains)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (Atlantic Ave/Barclays Center station; Manhattan bound N, R, Q & D trains)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (Spring Street station; downtown 6 train)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (33rd Street station; downtown 6 train)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (Astor Place station; downtown 6 train)

Riddles in the Dark - Voiceless it cries, Wingless flutters... (2015)

Answer: The Wind.