User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-5043481-20121025183252/@comment-125.165.93.249-20121029040204

Remains of ancient civilization where intellegent being beside humans has been wiped out by the monsters...or Elder Dragons.

(Since the level of structure looks like they're created in Bronze age or something...but hey, we have those Ancient series-weapon that look somehow futuristic, right?)