General comments:

In the top right hand room (see map) you'll find a Silver Key guarded by a lone Nightmare. Yes a floating fish with whiskers! Don't let that appearance fool you though... they have big nasty pointy teeth. ;-)

If you happen to get to close to a Nightmare when you kill it you'll take damage and if you're low on health you'll most likely see this.

No guesses as to what the Silver Key does.

Conversations with the Dead:

Read the Conversation with the anonymous German soldier (bottom of map).

It's worth quoting the Official Hints Book about this dead guy:

His elevator doesn't go all the way to the top. He's a couple of beers short of a six-pack. All his dogs aren't barking. He's a couple of cheerleaders short of a squad. He's a loon.

Or is he? What does he know? Our name? What is he hiding? What is our name?

Items to find:

Siver Key (one point + $9.2K).
Walther P4 Pistol (beside body).
Twelve Walther P4 Magazines (one loaded in the pistol).
Copy of Mein Kampf

Points to note:

When you pick up the Silver Key your points will increase from 11 to 12 and you gain a further two health units bringing your total health to 12 units.

In the room with the ladder that takes you down to "We Can See In The Dark... Can You?" you'll see ten pillars yet in map view there are only nine displayed. A secret pillar perhaps leading to a secret room? There is an odd vacant area behind that pillar.

Monsters to kill:

Ghouls, Zombies and a Nightmare.

Decision to make:

You see crystal ladders going up. Ascending to Wrong Way!.

You see a crystal ladder going down. Descending to We Can See In The Dark... Can You?.