As noted by @georgecmu, drones for mapping underwater caves have been used for many years--evolving to autonomy from hand-held & scooter-mounted LIDAR mapping a

As noted by @georgecmu, drones for mapping underwater caves have been used for many years--evolving to autonomy from hand-held & scooter-mounted LIDAR mapping arrays. Barbara am Ende wrote a 2001 article in Computer Graphics on such efforts (paywalled: https://www.computer.org/csdl/mags/cg/2001/02/mcg2001020014.html https://www.computer.org/csdl/mags/cg/2001/02/mcg2001020014.... ). I am aware of a variety of drones that have been deployed in air-filled caves too--from cameras on balloons (tall chambers with high leads) and standard copter drones to rubble-searching robots. Tethered cameras are occasionally used to evaluate obstructions (e.g. narrow cracks and breakdown). Overall, though, in-person exploration is satisfying and compelling. Robotic tech in air-filled caves mostly is used either for demonstration purposes or, in rarer cases, to determine the best locations to exert more human effort. Another branch of study is the discovery of subsurface voids from the surface using ground-penetrating radar, microgravity, electrical resistivity, or other geophysical methods. A robot could be equipped with the sensors in dangerous or inaccessible locations, such as off-planet or war zones. DARPA had an interest in this in the early 2000s to locate hostiles in caves, though I do not know its current priority.