Delta Green knows the score:
#DeltaGreen knows such tunnels run beneath cemeteries and connect far places by strange geometries. #notsloths https://t.co/BgFL7HniGJ
— Delta Green (@DeltaGreenRPG) March 31, 2017
Although you don’t have to go full Mythos, there. Cryptozoology works just as well. Giant South-American Mega-Ants could work, for example. Especially if you could tame and ride them while wandering around the Amazon.
But, yeah: given the claw-marks, you probably have to go full Mythos.