Complex sentence: Many other minor settlements also exist as well as containing ruins of past civilizations, the biggest of which being the ruins of Vendigroth, the most advanced city on "Arcanum", which met a sudden and mysterious end.
Split into simpler sentences: Many other minor settlements also exist, as well as containing ruins of past civilizations. The biggest of these is the ruins of Vendigroth, the most advanced city on "Arcanum", which met a sudden and mysterious end.