Hello again!

Below is a rough outline of what might be expected as one ventures deeper into the tunnels. Please let us know if you have any further questions!

Level 1 - first 500 yards or so
Wall Movement: Minimal. Closer to the entrance, the walls don’t shift around quite as much. It seems that a regular exit of some description is maintained at a short distance.
Lighting: Declines quickly from the immediate entrance.
Creatures: Few. Mostly animals that have wandered in from the plains. The occasional distressed rabbit.
Hazards: Trips, slips, nothing too dangerous.

Level 2 - 500 yards to 1 mile in
Wall Movement: Nothing too dramatic. You will often hear things shifting around in the distance, but it isn’t yet to the point of walls slamming across to block the space you just walked through. Overall, while it doesn’t feel entirely dangerous, it feels creepy, like someone staring at you from the other side of the room.
Lighting: Hope you brought a torch.
Creatures: Nothing. Nothing from the outside is daft/brave enough to come in this far unless it’s trying to die, and nothing from the inside tends to come out this far.
Hazards: The floor is a bit crumbly here, and the shadows make sudden drops hard to see. At times the roof drops low enough to skin your forehead if you aren’t watching where you’re going.

Level 3 - 1 mile to 3 miles in
Wall Movement: More active. You will see the shifting happening directly in front of you, blocking paths you were about to take, and at this point navigation difficulty begins to rise on a sharp curve. There seems to be a pattern to the movement, if you can stay for long enough to work it out, but the lack of lighting makes it doubly difficult.
Lighting: The walls here are slightly damp and the moss growing on the walls produces its own pale bioluminescence. It’s a sickly blue/green colour, however, which doesn’t really do much except make it difficult to see where the walls actually are. Disturbing it results in a release of fine spores that make it difficult to breathe.
Creatures: While actual encounters would be rare until the deepest parts of the tunnels, where they widen out and occasionally become caverns in their own right, it would not be unusual to find traces of the larger beasts that roam around those areas. It looks like they are trying to get out, in some places, but the tunnels quickly become too narrow for them to get any further.
Hazards: Darkness, deep drops in the path, sudden narrowing of the path or dropping of the ceiling. The tunnels can get unstable in places and the movements of the walls make this worse.

Level 4 - 3 miles to ???
Wall Movement: Very active, almost violent at times. Walls seem to deliberately shift to block you and sometimes feel they have the intent to hurt you, slamming across where you were just walking. At this depth, reliable navigation is all but impossible and going back the way you came becomes increasingly difficult.
Lighting: The bioluminescent moss becomes more prolific as the walls and floor become more consistently damp. There is usually some kind of dripping sound from somewhere.
Creatures: Everything you ever feared was hiding under your bed is lurking around in this place. Whether they were put there or evolved there is up for debate, but they are there nonetheless, and they don’t like the fact that you’re there too. Due to their size, they are at least not numerous, but the largest beasts are not the only things lurking in this darkness.
http://img11.deviantart.net/7a1b/i/2009/018/b/7/cave_monster_by_loztvampir3.jpg
http://orig09.deviantart.net/1876/f/2012/299/f/3/monster_in_a_cave_by_khezug-d5j179t.jpg
http://orig04.deviantart.net/0967/f/2011/353/8/4/cave_creature_by_cebob-d4jjmmw.jpg
Hazards: Sheer dropoffs, hidden pits, "puddles" deep enough swallow a person whole. This isn’t the kind of place you want to be if you value your life, or are woefully underprepared. Pressing on (and not dying) will lead the intrepid explorer to a massive cavern hosting a large underground lake.