The Secret Fire RPG. It's titled (in a style reminiscent of the old TSR numbering system) "X1 The Rings of Death."
To give an idea of what it's about, I offer up the introduction. This reveals slightly more than what characters know at the start of the adventure, so if you suspect you might face the Rings of Death as a player sometime, read on at the risk of spoiling a bit of your own enjoyment at uncovering the mystery surrounding the rings.
The Rings of Cernossen have stood for millennia. They were raised by a race of men that ruled this part of the world thousands of years ago. These kings were among the first to learn the secret of iron. With it they dominated their neighbors, drove the marauding, blood-worshiping beast men into the forests and bogs, and cemented their rule.
The great hill and its hollowed-out heart were sacred to this tribe. They erected the stones to honor their tribal deity Cernossen (a being who drew its power from the Elder God of Life), the antlered entity that brought fertility and abundance to their plains. Over the centuries, the tribe carved tombs from the hill to hold their royal families and further catacombs where priests could carry out rites to Cernossen.
No society of men lasts forever. The song of iron spread until even the beast men could sing it. Armed with the weapons of their enemies, the beast men’s raids grew bolder and bloodier. In just a handful of generations, the human tribes were crushed, their remnants scattered, and their long history of accomplishments forgotten.
Like the humans before them, the beast men were drawn to the mystery of the sacred hollow in the hill. They, too, revered the power of Life, but their methods were dark and sinful. Vile and bloody sacrifices transformed the hill from a shrine where life was holy to one where life was served hatefully and spilled with abandon.
A thousand years later, the beast men are weaker and fewer in number, and once again forced to live in the bogs and forests by the advance of other races. They still make pilgrimages to the stones twice each year, on the Spring and Autumn equinoxes, though even their oldest shamans don’t entirely remember why. It’s on the eve of such a pilgrimage that the player characters begin their exploration of the stones and the surrounding catacombs.
The map extract shown here is from my hand-drawn turnover, not the final version, obviously. It shows the hollow at the center of the hill where the standing stones were erected, plus the entrances to the tunnels into the surrounding hill. Yes, the physical arrangement is a tad reminiscent of the Caves of Chaos. That's not a coincidence. The resemblance to B2, however, pretty much stops there. What characters find when they explore these catacombs is very different from what resides in the Caves of Chaos.
Celtic and druidic myth was a big inspiration for this adventure -- no surprise, considering the Stonehenge-like artifact at its core. Inspiration is a funny thing, though. The Celtic notions served chiefly to focus my ideas. If the standing stones were replaced with Egyptian obelisks or Aztec stele, most of the adventure could be reflavored to match without breaking a sweat. Ancient rites and the restless dead are conveniently cross-cultural.
"The Rings of Death" is scheduled for release right around Halloween.