Atmosphere is one of the key ideas in contemporary aesthetics. The concept proves to be exceptionally useful whenever particular spaces, including interiors or urban spaces, are discussed regarding their unique features. The goal of the paper is to reconsider how an urban atmosphere may be understood. In order to do that, we will shed light on the ontological nature of atmospheres, by revisiting the concept as it recently was presented by some influential proponents of the aesthetics of atmospheres. Contrary to the widespread view, we argue that an atmosphere is not an entity itself. It is not a “quasi-thing” or “half-thing,” as usually stated, but rather a relational feature of a given site that exists only when it is experienced by someone. At the same time, our discussion of the metaphysics of atmospheres will provide us with a better understanding of the idea of urban atmosphere as characteristic of a particular site. Moreover, the ontology we will sketch allows us to consider the idea of an atmosphere of a whole city.