The Caverns of Thracia (1979)

From the back cover:

They Have Been Waiting.

For over a thousand years the things that lurk beneath the waters, skulk in the darkness and lie hungrily in dank crypts have been patient, while all around them men and monsters bicker amongst themselves, bold enough to traverse the dark caverns' depths, but afraid or perhaps wise enough to leave the forgotten vaults and hidden passages alone.

And still, they wait, undisturbed. They are waiting for you!

User summary:

This module is billed as an official dungeon approved for Dungeons and Dragons. It contains over 100 detailed room descriptions on four levels. The module may be played by characters of level one and up and the expectation is that players will flee from the darker terrors within if they are unready to face them.