The Other Side is a dimension of the deceased that is superimposed with the world of the living. Within it are also some form of gateways that lead elsewhere yet unknown. It may be a dimension where the dead temporarily linger before moving on to another; however, no concrete findings support the theory .
Dark London is the Other Side version of London. It is a colloquial term used by a number of characters. Additionally, a book titled "Dark London, an Interim Cartography" is in the possession of the Orpheus Society. 
The Other Side physically resembles the living world, like a replica, with a few differences.
The place is deadly chilly. All surfaces are covered by sheets of icicles which quickly envelop a surface that had its icy cover brushed. Mists drift over the land and moves independently. All movements of any kind in that side, except if made by a visiting living person, does not produce any sound. Wind and water does not exist. Areas where bodies of water should have been are empty. Even animals are nowhere to be seen. Physically, some structures look larger than the ones in the living world. And supposedly rigid things seem to bend, contract, and stretch.
Permanent dimness, dark as nighttime, consume the place. No light, electrical or natural, in the living world is replicated there. But, some illumination comes from the sky, that is however without stars and moon, that somehow touches areas that a light from above could not have reached. Even electric light coming from a visiting living person's torch is dimmed down and flickers.
Time becomes tricky in that dimension with no daylight. It is felt to pass but not by how much. A few hours felt could have been a day in reality.
And, to top it all off, it is filled with the dead - the lost souls whose voices can be heard by anyone with or without a Talent . Although during Marissa Fittes's time, souls who were ready to cross to another place were also trapped in the Other Side due to Marissa's devising. Devices used to deal with the ghosts (i.e. swords, iron fillings, etc.) in the living world does nothing to the Other Side's dwellers in their own dimension.
All over the Other Side are vague black yet shimmery things that are described differently (by different characters) to be like cracks, fissures, black gates, black doors, black pools, and curtains. These things are the portals that take the ghosts to another place from the Other Side.
- ↑ The Empty Grave, VI: The Beginning, Ch. 28: " Theorized by George Cubbins: “Getting back to my theory ,” George went on, “I think the spirit passes through those door things—however you want to call them—and reaches yet another London, but this one’ s shining with light….”"
- ↑ The Empty Grave, III: A Body in the Street, Ch. 15
- ↑ The Empty Grave, IV: The Siege of Portland Row, Ch. 22: " "The spirits could not speak, but that didn’t stop them calling out to us, hooting and crying like owls. As a Listener , I’m used to such stuff, though it was strange to hear it in the silence of the Other Side. It disturbed the others more than me. T o their surprise, they found they could hear it, too.""