Why would we strive for new realms to explore? The motifs of the mythic are so strong in those otherworldly locations that we wish to experience them through our characters. These are the worlds that are stranger than strange and uncomfortably real as science continues to push the boundaries of what we believe to be possible. Where rational thinking and science tell us we cannot experience a thing due to its hazards, our heroes laugh and invite us to enter their worlds through their bodies. These otherworldly locales we dream of are not merely the imaginary realms where kings and peasants live in a simulacrum of our existence. No, the places of existence that most fascinate us are those where the physical reality is quite different than ours. They serve as the homes of gods and devils, elementals, and myriad creatures as of yet unknown. Simply put, these places allow our imaginations to go wild. Here, nothing we conceive of is impossible. Cosmos Builder provides fantasy cosmologists the tools to create a unique depiction of the realms above and below (and everything in between) that can be incorporated into any setting. This book presents a great many options for the game master to append to preexisting or newly conceived settings. While this book cannot include all possible options, it hits upon the most common elements of planes of existence and offers insight for deviating from and blending these elements to suit your needs, to craft new dimensions and the strange worlds that exist on them and where diverse dimension meet. This book is a toolbox, filled with ready-to-assemble components that will allow you to quickly flesh out your vision of a cosmology. These tools are designed to let you to share your vision with others so they can adopt your cosmology (or portions thereof) to their campaign, regardless of which game system they use. The only thing they require is knowledge of how the tools in this book work, or an explanation from you about how your f