The Shadowlands is the spiritual world of the Thomas Book series. The shadowlands is the land of the dead, a place of spirits and echoes of old buildings and memories of the past and present.
The Shadowlands is full of ghosts but is held perpetually in a state near midnight where the only light source is that of the moon.
Ghosts will commonly stand near the echoes of their homes or the places where they are drawn until something gets their attention.
The most common source of attraction for a ghost is that of a life spark. Any living being that crosses into the Shadowlands will eventually draw ghosts. Thankfully, the ghosts aren't too quick so you have a while when you're moving around in the Shadowlands. The problem is that the arrival of a life spark will draw every ghost for miles given enough time. They become the moaning mass of zombie-like entities that are drawn to the energy of the living being, who will also give off a faint, almost lunar glow - rather like someone wearing white under a black light.
Ghosts have been known to attack in mass and pull the living apart to just get a taste of the living energies that they once held.
They are not, however, the worst things out there.
Wraith are flying, vengeful ghosts that can suck the life energy out of someone with a touch.
When entering the shadowlands - a common tactic is to cast a spell that will mimic the life spark in another location to distract the mobs of ghosts and the wraith that attack in swarms. They are the equivalent to a 'Thumper' as they mimic the thump-thump of a heart beat.
Entering the shadowlands is dangerous but it is also very useful. A mage's magic is stronger in the shadowlands. They are able to create gateways and bridges to connect various points in the Shadowlands thus allowing them to travel at great speeds in the mortal world.
By the creation of a gate and a bridge, a mage would be able to travel 1 mile with each step, or 10, or even a hundred depending on the strength of the gate.
The creation of a gate and a bridge takes some time, approximately ten minutes for a quick bridge, longer for a stronger version.
Entrances into the Shadowlands are not too difficult to come by if you know where to look. Learning how to make a slit in the membrane that separates the real world from the Shadowlands does take some effort of will. You also have to be careful where you cross over. The doors to the Shadowlands are known because they're usually the safest places to enter - the place where the membrane is the thinnest and easiest to step through.
Making a door, even a temporary door, is dangerous because while it's open things can come and go both ways. Normally, the membrane will seal itself over almost like a cut healing. Given a few moments the 'injury' will start to close on its own. It would take effort to keep it open.
It is not impossible to make other doors or even, if the Cabal were strong enough, punch your way into the Shadowlands - though the door would have to be watched.