There is a pleasant difference in this delving, the PCs are exployers, cartographers, rather than going in for the loot. I think that is a nice touch Taronga.
Some natural hazards within the mines...
Poison Gas - aka methane, leaks up from the earth, miners would take canaries with them into the mines because the poison gas would kill the small bird quickly, and give the miners a chance to escape before they were overcome with the fumes. (This is not the case now, there are mechanical gas detectors) The gas is also explosive!
Scaling - similar to a cave in, this is a large piece of ceiling deciding it needs to be floor. Can partially block tunnels, squish people, that sort of thing.
Darkness - there is NO light underground
Small squishy bite-y things - more than likely white and eyeless, poisonous to nail rare prey, certainly enough to make an explorer sick.
There are some more mundane ideas, I am sure some of the others can help with the more fantastic, if they don't I will. Go to Comment
In addition to the possible plot lines behind this... try looking into the Demon Gates sub, as this stated that demonic beings or creatures came out of the activating of the mechanism... Awesome idea. Go to Comment
Natural Hazards- Rock slides, tunnel collapses, poisonous gas vents, water-filled passages, radioactive mineral deposits, impenetrable darkness, pressurized wind tunels, bottomless crevices.
"The Bleeding Door". An two-foot thick Obsidian gate, carved from the surrounding rock, leading into the ancient dust-filled dwarven crypts. Drops of blood ooze from it, coagulating on the floor beneath it. (what it does is up to you).
"The Beard Golem". A hideous creature woven from countless dwarven beards, and ensorcelled to defend the inner catacombs, shambling among the empty halls. (holy crap! I might have to write this one up into a submission!)
"Dwarven Vampire". The rare and deadly dwarven vampire is not often expected by adventurers. This creature is the last of the dwarves!
"The Curse of Hawmeggora". A curse layed on a specific area. Once entered, the trespassers begin to slowly but irrevocably turn to stone over the course of the next several weeks.
Moon Hunter, thank you for the advice and for the mark.
I didn't expect such a high one - a very pleasant surprise!
By the way, I gave this module to my players and they liked it. The most interesting was to watch them drawing caverns and the dungeoin itself! Three of the six were doing it in turn and three times they had to re-draw the main dungeon level. :) Go to Comment
Within a kingdom the prince or princess has died or been killed and the Queen has been driven half-insane with grief.What if one of the PC's was mistaken for the dead prince or princess and not allowed to leave? There would be advantages in accepting the role, but would it be worth it?