Head-mounted displays can offer personalized immersive virtual reality (VR) training for patients who have suffered an Acquired Brain Injury by tailoring the complexity of visual and auditory stimuli to their cognitive capabilities. However, how these virtual environments should be designed remains undetermined. We conducted a participatory design workshop with eight neurorehabilitation experts to collect their opinions on using immersive VR-based neurorehabilitation and co-create examples of low and high-cognitively demanding immersive virtual training environments. Participants highlighted the importance of developing meaningful and realistic environments. This study provides an example of a high-tech co-creation workshop whose results provide insights into designing training environments in immersive VR to meet patients’ needs.