Help with dungeon creation ideas

Here are some basics. To make an interesting section of the dungeon,
vary one or some of these features in that section. But try to keep
everything else a standard. The early parts of the dungeon should be
standard, with later parts varying more based on how far away they are.

Surfaces: (Standard: Cut blocks, cool, damp)
Rough hewn stone / smooth polished stone / carved / mine-tunnel (hewn stone with wooden supports)
Freezing / Cold / Warm / Hot / Searing
Dessicated / Dry / Moist / Dripping

Foliage: (Standard: Slight slime)
Nothing / slimey / mossy / mushrooms and fungus / small leafy plants / phosphorescence

Temperature: (Standard: Cool)
Freezing / Cold / Warm / Hot / Searing

Noises: (Standard: Echoing)
Magical silence / Silent / Faint tapping / moaning / dripping / running water

Smells: (Standard: Musty)
Smokey / rotting flesh / rotting plants / sulphurous / acrid / sewer

Light Level: (Standard: Dark)
Torch sconces (lit/unlit) / melted candles / creepy glow / floating lights / everything glows / magically deep darkness

Air: (Standard: Stale)
Poisonous / bad-tasting / fresh breeze from surface / breeze from below / misty / ozone / explosive gasses

Ceiling height: (Standard: 10')
Crawlspace
(small creatures crouch, medium crawl, no larger), short (5', large
creatures crouch), very high (20'), cavernous (30')

Hall Width: (Standard: 10')
Very narrow (small creatures or smaller), cramped (5'), broad (20')

Moisture: (Standard: Damp)
Flooded to ceiling / neck-height / hip-height / knee-height / ankle-height

There are probably more features you can identify to vary.

Now you can add in things like secret doors, locked and/or Wizard Locked
doors, traps, puzzles, tricks. Really go out there, including things
like elevator rooms that travel between floor without people noticing,
or rotating rooms that reveal different hallway exits depending on their
position. Large water-traps.

Place monster lairs all around, in
places where you think monsters would like to lair. Then put those
monsters on a random encounter list along with entries for strange
happenings (like a gust of wind coming through that extingushes all
torches). Have one entry on your random encounter table for a creature
from one level above (from outside, if you're on Level 1) and one entry
for a roll on the table for the level below.

Remember that as a
mystical and strange Underworld, the doors will open for resident
creatures but not for PCs. The monsters probably also know about some of
the secret doors, and will use those that they know of. There can also
be connections between rooms that the PCs can't use (say, passages full
of life-draining blackness, which Undead can use but PCs won't want to,
or tiny tunnels that the Giant Rats can use but PCs are too large for).

Place
large groups of monsters in large rooms, and individual monsters in
small areas. This puts them at the utmost tactical advantage, which they
would likely choose for their lairs. Make sure the lair has a way to
get out to the dungeon exits up and down without running across a trap -
unless it's a trap that those creatures set (such as kobolds with
tripwires or spiders with webbing).

Concentrate the loot in the
lairs, but leave some scattered around elsewhere. The goal of the
adventurers is to get the loot, which means outsmarting or sneaking past
or defeating the lair's guardians. You should also put treasure behind
trapped areas or under puzzles, as these are unlikely to have ever been
opened by the residents.

Make sure you use elevation in your
dungeon. Have rooms that plunge down an entire level (without an exit
into that level) and the PCs must negotiate their way across somehow or
else find another way around. Have ledges higher up, or pits, with
interesting things in them. Creatures with missile attacks will favor
such places, as they can fire downward with impunity upon creatures who
have no missile attacks.

Draw your map for a level, making sure you have a couple ways in and a
couple ways down to the next level. You can have a passage down skip a
level, so it goes from Level 1 straight to Level 3 for example. It's
also fine to have many passages be hidden behind secret doors or debris
or something.

Mix up the treasure. Don't just have coins and
magic items. Consider rolling a percentile die, and that is the
percentage of any coinage treasure that is instead in some other form.
That non-coin treasure could be in gems and jewelry, salt or other
spices, fine oils, incense or perfume, fine clothes or whole cloth,
books, toys, nonmagical armor and weapons, useful adventuring gear. Also
consider changing certain coin treasure hoards into some other
denomination that is less or more useful. For example, a treasure of 200
CP and 300 SP could be turned into 200 Bronze Agols and 300 Silver
Smerduks. The value is equivalent, if they bring them to the
moneychanger, but they need to pay a 20% fee on it. Or perhaps small
bars of metal, carefully wrapped as if the owner intended to return for
them someday ...

You can draw out maps ahead of time, partial
maps of a level that show the exporations of some long-ago adventuring
group. These can be given away to the players as treasure, for is not
knowledge about the dungeon a treasure? The maps can occasionally show
some symbol the players must figure out, or show a secret door they may
not have found. The maps might also be outright wrong!

This is a
difficult thing, but try to think of ways to include encounters where
the players don't have to fight. That is, if they are bloodthirsty, they
will try to kill everything regardless. But if they are clever, they
could get more out of the encounter by talking and thinking than by
destroying it.

Include areas of each level that are beyond the
abilities of the PCs to breach. For example, a Wizard Locked door on
Level 1. They can easily return to it later, but the first time they
encounter it they may not be able to open it. The barrier could be a
special lock or spell ward, or perhaps a very tough monster that doesn't
move around much (golems are great for this, Undead too). And if they
figure out some way to get in, that's fine.