Museum fatigue is the physical, cognitive, and emotional exhaustion that visitors experience during museum visits. This represents a significant barrier to the educational and restorative potential of museum environments. Despite decades of research identifying environmental contributors to fatigue, no standardized tool exists for evaluating how museum design supports or hinders restoration. This study developed and preliminarily validated the D.R.E.A.M. tool (Designing and Assessing Restorative Museum Environments), a 42-item tool informed by Attention Restoration Theory. Through a three-phase process consisting of a literature review, expert content validation with 21 museum professionals, and visitor-based validation at The Herbert F. Johnson Museum of Art with 20 participants, the tool demonstrated solid content validity and alignment with visitor-perceived restoration. Key findings highlight natural light, seating placement, wayfinding clarity, and emotionally supportive spatial design as critical environmental determinants of a restorative museum experience. The D.R.E.A.M. tool offers museum professionals a practical, evidence-based way to better understand and improve the restorative quality of their environments.