The United Kingdom’s railway network extends to over 20,000 miles of track and more than 40,000 tunnels, viaducts and bridges. Much of this infrastructure was constructed in the 19th century and needs to be continuously monitored to ensure its safety. One particular challenge is the development of hidden voids above railway tunnels that are at risk of collapsing onto the track. Cosmic rays present a unique solution to this problem, by providing a way to non-invasively survey the internal composition of large structures using only natural background radiation. The Geoptic team has recently demonstrated this technique can accelerate the identification and characterisation of voiding above railway tunnels. We are now looking at applying the technique to survey other critical infrastructure. In this talk I will discuss the benefits of cosmic ray imaging and the technical challenges faced when using it to survey large heterogeneous structures.