IntroductionOlder medical patients (>65 years) represent 54% of the admissions to Danish medical and emergency departments. Acute admissions and bed-rest during hospitalisation are independent risk factors for death and dependency in older patients. Even short hospitalisations are associated with increased dependency in activities of daily living after discharge. Interventions that increase mobility during hospitalisation are therefore important. The purpose of this protocol is to describe the intervention design of the WALK-Copenhagen project, aimed at increasing 24 hours mobility in older medical patients during acute hospitalisations and following discharge.Methods and analysisThis study is based on ethnographic fieldwork and interviews. Workshops are used to develop and co-design the intervention in collaboration with key stakeholders (patients, relatives, health professionals and researchers). The theory of cultural learning processes, and the cultural historical activity theory will be used to help us understand the interaction between health professionals, structures and objects in relation to mobility in the medical departments.Ethics and disseminationThe project will adhere to the directives of the Helsinki Declaration. Ethical approval was not required for the study since formal ethical approval is not mandatory for studies that do not involve biomedical issues (I-Suite no: 05078) according to Danish law. Informed consent was obtained for all participants. The results will be disseminated to health professionals, managers, patients and relatives, who will be invited to afternoon meetings where the project will be discussed. The results will be published in peer-reviewed scientific journals and presented at scientific conferences.