Over the past years we have witnessed an increase in psychedelic retreats, including legal psilocybin retreats in the Netherlands, Portugal and other places. People attend these retreats for a variety of reasons (e.g., religious, therapeutic, recreational) and the retreats differ strongly in their overall approach to set and setting. Research in retreat settings affords less experimental control compared to lab-based studies. It also places ethical and legal challenges with respect to setting up collaborations and research and can create conflicts of interest. At the same time, research at retreats offers a highly ecologically valid setting and using pre-post longitudinal designs one can gain intriguing insight into how psychedelics are used ‘in the wild’. This presentation will provide an overview of some of the lessons learned at the University of Leiden in collaboration with psychedelic retreats in the Netherlands and abroad. We will highlight challenges and opportunites as well as practical recommendations for conducting field studies with psychedelics. We will highlight two examples of retreat studies: a qualitative study assessing belief changes in religious leaders and an fMRI study assessing changes in neural activation patterns associated with attending a psychedelic retreat. Next to allowing us to answer new scientific questions,  insight into the naturalistic use of psychedelics can also inform the general public about potential risks and benefits associated with retreats.