Carcosa is the conclusion of Kevin Watson's Haunting of Hastur series. At the end of the previous adventure, the party stopped the cult of Hastur from building a vessel that would bring the Old One into the world. That adventure ended with them being engulfed in magical energy.
Carcosa sees the players waking up in the Carcosa Complex, a demiplane of madness connected to the Old One.
Kevin gave me a sneak peak at the adventure and I have to say, this one is pretty unique. The party has 24 hours to find a way home or be bound to the Carcosa for ever. This isn't the only way they can find themselves permanently trapped. If they die, take a long rest, or sleep, they are bound to the plane. The party starts fully rested with all abilities. The special rules of Carcosa are clearly outlined in a side box. There are several encounters and most are primarily roleplaying. While fighting can happen, the denizens of the Carcosa aren't particularly inclined to fighting the pc's. There are four demon lords that rule the various parts of the complex. Each is unique and fleshed out. They all have their own motives and can help or hinder the party. The encounters are varied and it will take a variety of skills and courses of action for the party to succeed. The adventure seems like it will be challenging, but not impossible. If you ask me this is the perfect way to end this series of adventurers.
The front and back cover art looks great as do the maps. The pdf I looked at was a work in progress, but the material looks solid. This is definitely a project to back and if you don't have the previous adventures you can add them (in pdf or print) as add-ons.