The sewers underneath the Hound Pits Pub.
Piero Notes Anomalies is an audiograph found in Dishonored, recorded by Piero Joplin.
Transcript[]
I am getting a frequency reverberation that confounds some of my experiments. I suspect there are some kind of empty chambers beneath this building. In a District this old, anything is possible.
Location[]
The audiograph can be found on a table in Piero's Workshop before the mission House of Pleasure.