From publisher blurb:
Every generation, the blood moon rises and a nightmare castle from outside reality emerges to blight our world. But what form does it take? How does it corrupt the surrounding landscape? And how will the heroes fighting it back make their way through it?
Terra Incognita is a system for generating nightmare castles for players to explore, in the vein of Metroidvanias like Hollow Knight, Castlevania, Legend of Zelda and Hyper Light Drifter. Using a deck of cards and the book's prompts, you'll build up the castle's wards room by room, decide how they all link together, and what monsters command them.
This book was designed for use with UFO Press' Rhapsody of Blood, but the castles it builds can be dropped into your dungeon-crawling tabletop RPG of choice (or even used as the map for your own Metroidvania computer game!). With support for top-down and side-on maps, optional systems for locks and keys and havens scattered across the map, Terra Incognita is the castle-building tool you've been searching for.