The National Trust cares for many places where access to heritage is restricted, for safety or other reasons, limiting the opportunity for monitoring, recording and visitor engagement. The remains of the Atomic Weapons Research Establishment (AWRE) testing facility, built between 1954 and 1962 at Orford Ness on the Suffolk coast of England, represent such a case. The AWRE structures are a Scheduled Monument and sit within a wider landscape of twentieth century defence heritage. The buildings have attained a mythical status in popular culture and attract substantial visitor interest. However, they are unsafe to enter, and their long-term conservation strategy is to allow their gradual decline to a point where significant evidence is lost, with their ultimate loss to coastal erosion anticipated. Recognising these challenges, our work has sought to develop and assess a prototype use of robotic and semi-autonomous survey technology for heritage at risk in challenging environments. A suite of complementary technologies, including Boston Dynamics quadruped robots, caged and conventional drones combining laser scanning and digital photogrammetry were used. This paper provides an account of practicalities, benefits and limitations of robotic and semi-autonomous survey for documenting heritage assets.