Complex sentence: The remainder of the group walk along the length of the hall exposed by the broken mirror, arriving at a room containing records, documenting the progress of the "subjects", among which were a savant, and an autistic individual.
Split into simpler sentences: The remainder of the group walks along the length of the hall exposed by the broken mirror, eventually arriving at a room containing records. The records document the progress of "subjects," among which were a savant and an autistic individual.