General comments:

"I imagine that right now you're feeling a bit like Alice, tumbling down the rabbit hole?"

Deep hole! Take a look at that elevation. You're 1042.4m below the surface. The last level was only 22.7m below the surface.

You're in a tiny room (see map). Feel those walls pressing in? Getting claustrophobic? Pull yourself together man! There are three teleporters but which one to take? If you take the facing one you end up in another little room (see map). The teleporter you arrive through will take you back to the first room. Thus there are four teleporters to explore, two in each room. It's easy to tell the two rooms apart since one has a saved game rune.

Both teleporters in the first room take you to the same place (see map) though this might not be immediately obvious since the teleporters are back to back. If you take one of the teleporters back to the relative safety of the first room and then return you'll find that the automapping feature has reset itself just as it did in The Labyrinth.

Staying alive down here just got tougher. Meet the Greater Nightmare and the Venomous Skitter. Deadly variations on a theme. The Greater Nightmare is immune to all ammo except the AK-47 SABOT rounds, 40mm Projectile Cartridges, and the 40mm HE Cartridges. Oddly the Official Hint Book states that Greater Nightmares can only be killed using SABOT rounds and Projectile Cartridges. Here are two quotes from the book:

The Greater Nightmare is five times more durable than its lesser cousin. In addition it has also developed two powerful abilities. First, it is armored. It can only be harmed using armor-piercing shells (M-79 Projectile Cartridges or SABOT rounds for the AK-47)

and...

40mm Projectile Cartridges- these don't do as much damage as the HE Cartridges and they don't affect multiple targets, like the Fragmentation Cartridges. So why would you use them? Because they are the only grenades that affect Greater Nightmares.

Not true! A 40mm HE Cartridge will also kill a Greater Nightmare.

Greater Nightmares also have an additional advantage in that their projectiles are guided as you soon learn from their death dialog.

Venomous Skitters as their name implies are poisonous. If they hit you with one of their green projectiles you'll not only take damage but you'll be poisoned. Just like when you poisoned yourself to avoid the Green Oozes, your health will immediately start to drop. Without the curative properties of the Clear Blue Potion you're going to die, albeit slowly. With dropping health you are also at more risk of dying from a few Skitter hits. As the level name says "Don't Get Poisoned".

Note that when you are poisoned you can't rest. The "no rest" dialog also suggests that the poison might wear off:

Find a cure or wait for the poison to wear off.

Unfortunately it doesn't so you'll need to use a Clear Blue Potion. You'll find two in each of the bottom corners of this part of the level (see map). If you're good you might not get hit by a Venomous Skitter however you should aim to come away without using one of the Clear Blue Potions. Not easy with Greater Nightmares, Venomous Skitters, and the odd Ghast thrown in.

The teleporters in the second room take you to the another part of this level (see map). Same story here. The automapping will reset itself if you leave. You'll find another Clear Blue Potion (centre of map) and a Pale Violet Potion (top centre of map). This is the second Pale Violet Potion found so far. The first was on "Warning: Earthquake Zone" but in the rush to leave you might have missed it. Examining the vial doesn't reveal much regarding its purpose. The only way to find out is to drink it. Down the hatch. Whoa!

You quickly lose all sensation in your skin.

Fortunately the Pale Violet Potion does you no harm indeed it's quite beneficial giving you immunity to all monster attacks for a limited period of time. Save these for later you'll need them. ;-)

Here's a tip. When testing any new potion or item do so directly after saving your game and make sure there are some monsters in the vicinity so you can observe any effects. Return to the saved game afterwards thus retaining the potion or item for later use.

Items to find:

Three Clear Blue Potions
Pale Violet Potion

Monsters to kill:

Venomous Skitters, Greater Nightmares, and a few Ghasts.

Decision to make:

You see a teleporter. Teleporting to Please Excuse Our Dust.