The “xeno” – “the other” – is a prefix found in such hyphenated bridge words such as xeno-poetics, xeno-politics, xeno-feminism, or xeno-architecture. Xeno is the other, the not-self. But who or wha tis this not-self and where is it? In contemporary architectural discourse we find an increasing interest in more-than-human justice, speculation, or realization: ontological or critical posthumanisms and new materialisms explore nonhuman agency and transhumanist or cybernetic posthumanists celebrate the (always coming) fusion of the technological other with the self in order to overcome nature’s imposed (mortal) limits. There seems to be two types of nonhumans, related to the different – and often opposing – understandings of posthumanism: the man-made nonhuman and the non-man-made nonhuman. The xeno seems to mingle with ideologies of the former. A monad – as found in different monadologies, such as Leibnitz’s or the theosophical – is the smallest part of a metaphysical entity. It is the invisible sibling of the, almost outdated and refuted, physical atom. The monad seems to be exclusively found in life, in the non-man-made. In my presentation I would like to speculate on the xeno_monad, a conceptual overlap of the man-made and non-man-made entity and where it is physically and metaphysically situated in architecture. Physically, we might find such speculative entity in either the weathering processes of ruination and decay (non-man-made) or in the digital infrastructures which make up an increasing part of our architectural matters (man-made). Metaphysically, we find it in human perception (does the nonhuman even exist without human perception?): it is found in the fear of losing control over(architectural) matters and (information) flows; it is found in the desire to project human shortcomings onto the other, the outside rather than the inside; and it is found in the spiritual, sometimes perversely mixed with the transhuman, desire to overcome human limitations.