Cyclopean
Etymology
From the Cyclopes, the one-eyed giants of Greek myth. Later Greeks, gazing at the colossal stone walls of ruined cities like Mycenae and Tiryns, could not imagine mortals lifting such blocks and credited the Cyclopes with building them. Archaeologists still call that style "cyclopean masonry," and the adjective now names anything of similarly gigantic construction.
adjective · /sy-kloh-PEE-un/
Massive and built on a huge scale, especially of ancient stonework made from enormous irregular blocks.
What it names
Architecture or structure so vast it seems beyond human hands — reach for it to convey overwhelming, primeval scale, especially in walls, ruins, and masonry.
Example
The dam rose in cyclopean tiers of concrete, dwarfing the workers who crawled across its face.
Related idea
Monumental suggests grandeur and lasting importance; cyclopean is specifically about crushing physical scale, the sense that something is too big to have been made by ordinary people.