In the last five to ten years, several science, technology, engineering and medicine (STEM) museums have been experimenting with new forms of public engagement, aiming to be places for curiosity-driven investigation of the cultures of science via multiple perspectives, bringing artists, scientists, researchers, clinicians, members of the public and others together. Yet these diverse and rapidly evolving sites lack a clear definition of their family resemblances – something we argue is crucial for better understanding, advocating, and evaluating what they do. As a starting point for this definitional project we propose ‘the house’ as a metaphor and framing device for public engagement in STEM museums, grounded in experiences at Medical Museion in Denmark and Wellcome Collection in the UK. We further suggest that a Goldilocks principle – the notion of lying between two poles of a continuum in a ‘just right’ position – captures several key features of what it is about the idea of a house that resonates with the approach to public engagement in these museums.