Forbidden Zone

The Forbidden Zones are areas of Cybertron in the Dreamwave portion of the Generation 1 continuity family.

It looks alot different on Sonic the Hedgehog

The Forbidden Zones are regions of Ancient Cybertron declared off-limits by the Council of Ancients "for safety reasons" prior to the Great War.

Fiction

Dreamwave comics

Believing that the Council was hiding something, Megatron infiltrated a Forbidden Zone and, descending through the scarred landscape, discovering lifeless tombs of another civilization far below 'Ancient Cybertron.' Route of all Evil (flashback)

Megatron discovered that the Council was using dogma and myth to cover up the truth of their origins.

From Teletraan I: The Transformers Wiki, a Wikia wiki.