Mammals’ resting sites (dens) are important features of their ecology. Eurasian otter Lutra lutra resting sites are strictly protected by UK and European legislation and are ostensibly identified from associated field-signs. This legislation is difficult to apply given the poor understanding of resting sites coupled with the lack of evidence supporting a field-sign signature. We aimed to use camera-trap data to identify resting sites, investigate whether field-signs differed between resting and non-resting sites and describe behaviours recorded on camera-traps that are associated with resting. An evidence-based approach to identifying resting sites of Eurasian otter Lutra lutra from camera-trap and field-sign data camera-trap data showed that otters frequently visited potential resting sites, characterised by a very short time within the structure (often < 4 min). Resting sites were characterised by longer durations (often hours) during the daytime and night-time. Based on these data, six of our 26 sites were identified as resting sites. Modelling suggested that no single field-sign had a clear association with resting sites. However, we found a hitherto unrecognised distinction between otter latrines (defecation sites) and spraint (scent-marking) sites, and that camera-trap observations of latrine behaviour and bedding collection were exclusive to resting sites. As bedding and latrines are not always visible, presence of either indicates a resting site but no interpretation can be drawn from their absence, so camera-trapping would be recommended to identify resting site status. Data simulations found that camera-trapping for 38 d in winter, followed by 38 d in spring, was the optimal approach for a 95% chance of detecting a rest across all resting sites. Ours is the first study to identify standards and expectations for surveys using camera-trap and field-signs at Eurasian otter resting sites. Our novel account of their resting activity facilitates better interpretation of legislation.