That seems really deep for people to have been living. I could see living twenty or thirty meters from the entrance to provide protection against the elements or predators, but 300 meters means you have to have light sources and ventilation for smoke.
Could they have? Sure, but it sounds pretty advanced for cave dwelling early man.
Scientists: Underground stone rings made by Neanderthals:
http://phys.org/news/2016-05-scientists-underground-stone-neanderthals.html#nRlv
Neanderthal stone ring structures found in French cave:
http://www.bbc.com/news/science-environment-36381786