Another four Secrets are stashed away in Southwark.
Secret #24 - Southwark
The music box is to the southeast of the viewpoint in the middle of the borough.
From the central viewpoint, look to your right (southeast) and you'll spot a building next to the tracks.
Drop down to the railway tracks and follow them towards the aforementioned building.
The music box is on the wooden platform on the side of the building, next to the railway tracks.
Secret #27 - Southwark
This Secret is to the north of the easternmost viewpoint in the area.
It's at the base of the green tank that you can see from the viewpoint.
Hop down and head around the right side of the tank to find it on a crate on the floor.
Secret #09 - Southwark
The music box is at the docks to the southwest of Waterloo Station.
Head west from Waterloo Station until you hit the road that runs long the river, then turn left.
When you reach pier 3, head through the open doorway to the right of the building's main entrance.
Go straight ahead and you'll spot the music box on a barrel to the right.
Secret #12 - Southwark
The last music box in Southwark can be found to the northeast of Waterloo Station.
You can see the building it's located on from the central viewpoint.
Head east from Waterloo Station until you reach the Y-intersection.
There's a red brick building here.
Climb up to the roof to nab the music box.