From publisher blurb:
Deep Carbon Observatory is an adventure for Dungeons and Dragons.
The adventure takes players from a town devastated by an unexpected flood, through a drowned land where nature is turned upside down and desperate families cling to the roofs of their ruined homes, hiding from the monstrous products of a disordered world, through the strange tomb of an ancient race, to a profundal zone, hidden for millennia and now exposed, and finally to the Observatory itself, an eerie abandoned treasure palace, where they will encounter a pale and unexpected terror which will seek to claim their lives.
The adventure is suitable for a lucky mid-range party, a stupid high-level party or an exceedingly clever low level party. It is difficult, with a meaningful possibility of character death. Should you find them, and defeat their guardians, the treasures of an ancient culture will be yours.
At the final point of the Observatory is a glimpse of another world.
Deep Carbon Observatory is about 90 pages long, 20,000 words with four maps and extensive artwork by Scrap Princess.
Stats are minimal and given for LOTFP but should be easily transferable into any simple D&D system.