The Rat Warrens
 |
An "introductory" level to the megadungeon that is the Mountain. I'm not going to pretend it's another Tomb of the Serpent Kings¸ but I think it does an okay job of teaching some basic dungeoncrawling lessons - carry lots of light¸ talk to everything¸ combat has consequences¸ it's okay to run from fights¸ et cetera.
It's meant to be played with the GROG and The Mountain at the End of the World Player's Handbook¸ but (like any OSR-y based-on-a-certain-popular-roleplaying-game-y thing) it can be adjusted with fairly little effort to pretty much any other system that you're familiar with. Of note I guess is that it doesn't include morale stats (I just use a Charisma roll) so maybe have morale be 7 +/- CHA mod (which gives ratmen 5 morale and feels appropriate) or assign it by fiat or something.
Adjusting it for a different setting is also pretty simple:
hobgoblins = humans i guess¸ maybe elves or dwarves or what have you
ratmen¸ bat men = goblins¸ kobolds¸ or just leave them as-is
elves (rooms 10-15 are ancient elf tombs but the assumption is none of the PCs know what the fuck is an elf¸ in case that wasn't clear) = ancient evil snake people or some other sinister long-dead empire
Cover art is public domain.