General comments:

This level contains the infamous suffocation room but more on that later. If you survive the double door ambush at the beginning check out that locked door in the room on the left (see map). Remember it.

At the bottom of map is a long wide corridor with pillars. Watch out for flanking Skitters and also for a few Ghasts who can shake and bake you long before you see them emerge from the dark. Behind the seventh pillar on the left is a Clear Blue Potion.

At the top right-hand corner of the map you'll find another door. Behind the door is a body... hmmm... but should you enter?

Step inside and the doors will close. Check the Message Window for a fun comment. :-) Welcome to the Suffocation Room. Of course you don't know this yet until you talk to dead guy. Who could it be?

Conversations with the Dead:

Read the Conversation with Pedro (top right of map).

Pedro, Juan, Javier, Carlos... as the names suggest this is the Spanish speaking group the Germans referred to. Remember on "They May Be Slow..." the anonymous German soldier told us:

A group of people passed through here years
ago and one of their group walked through
the opposite wall of this room. I don't know
how he did it.

and...

They were speaking Spanish. I couldn't tell
where they were from, specifically.

Later on "Feel The Power" when we ask Walter about the gold key Muller had given him he reveals:

I had the key, but someone took it. A group
of people passed by, speaking Spanish, and
their leader took it.

Pedro claims that he died by suffocation yet he's lying in a pool of blood. His own? Did he committ suicide?

The suffocation room is a tough puzzle. Pedro tells us that the doors will eventually open but only after the air is used up:

I know what's going to happen now: you're
going to suffocate here, just like me. The
doors won't open for hours.

and again:

Long after you've used up the oxygen in
this tiny room, the doors will open. Just
like they did after I died. They will open and
wait for someone else.

Since you don't have an oxygen supply you're going to have to think of another approach. Time to explore that inventory more carefully. With a little judicious experimentation you should discover that the Red Cloak found on Happy Happy, Carnage Carnage makes game time pass more quickly for the wearer (1 minute of game time passes in 30 seconds of real time).

There is enough air in the room to last 2 hours but the doors won't open for another hour. If you wear the cloak the three hours will pass in half that time. Thus you'll survive. Resting at the same time just speeds the whole process up.

Of course solving this puzzle for the first time is another matter.

Points to note:

Earthtopus <andrew.malcovsky@gmail.com> writes:

A funny thing about the doors. Pedro says "They will open and wait for someone else." But the doors are closed when you get there, and stay open once you've beaten it. You can in fact run back into the level proper (I did once to save to see if I could). I will check on the way out if the trap resets but I have a feeling it doesn't.

Items to find:

AK-47 Assault Rifle (with empty clip) on Pedro (worth one point)
Clear Blue Potion

Monsters to kill:

Skitters, Ghasts, and Sentinels

Decision to make:

You see a vine ladder going down. Descending to Warning: Earthquake Zone.