Complex sentence: The northernmost group, designated as Group A, is clustered in a wooded hilltop and includes a pyramid standing over high with a long structure similar to a palace, at least, to its north-east.
Split into simpler sentences: The northernmost group, designated as Group A, is clustered in a wooded hilltop and includes a pyramid standing over high. A long structure similar to a palace, at least in length, is situated to its north-east.