  Digital documentation of large interiors of historical buildings is an
exhausting task since most of the areas of interest are beyond typical human
reach. We advocate the use of autonomous teams of multi-rotor Unmanned Aerial
Vehicles (UAVs) to speed up the documentation process by several orders of
magnitude while allowing for a repeatable, accurate, and condition-independent
solution capable of precise collision-free operation at great heights. The
proposed multi-robot approach allows for performing tasks requiring dynamic
scene illumination in large-scale real-world scenarios, a process previously
applicable only in small-scale laboratory-like conditions. Extensive
experimental analyses range from single-UAV imaging to specialized lighting
techniques requiring accurate coordination of multiple UAVs. The system's
robustness is demonstrated in more than two hundred autonomous flights in
fifteen historical monuments requiring superior safety while lacking access to
external localization. This unique experimental campaign, cooperated with
restorers and conservators, brought numerous lessons transferable to other
safety-critical robotic missions in documentation and inspection tasks.
