the.com/subterranean
Where the action happens underground, whether you mean caves or conspiracies.
means Existing, occurring, or operating beneath the earth's surface, literally or figuratively.
from From Latin sub (under) plus terra (earth), surfacing in English around the 1600s to name what dirt politely hides.
Sister wordTerrestrial shares the same terra root, just above ground.
Figurative useHidden motives and movements borrow the underground metaphor.
Deep cousinsSubterrene means even deeper, fully within the earth.