Beyond the Black Sea Adventure Area 4: The Skull

From publisher blurb:

The characters have found themselves on a strange scree slope, besides an impossibly high mountain. A green aurora dances overhead in a starless sky. High above black clouds swirl and circle, there is no light, the unfamiliar smells of fungoid entities is on the wind. In the total darkness, the only light your characters see is a glowing pillar in the distance and in the dark hungry beasts yawn and gnash chitinous incisors.

This adventure area can be used as a springboard for a horror campaign set on the alien world of Carcosa or could lead to some place in Stygia, the Nameless City or anywhere of your choosing.