FRench(?) TV/movie-80's-collapsing platform in the side of a rock/mountain

I’m looking for a film or series it might be French as I saw this on French television (Belgium RTBF) and I remember a scene where a person was trapped in somekind of chamber high in the rocks with 1 open side (small mountain site?) And the floor was very slowly collpasing upwards. so eventualy this person would fall down (to his/her death). In another scene you could see people (one or more) haning in trees. I was like 8 yaers old and I saw it around 1985-1986 I guess.