ABYSM

• Bottomless pit

• Deep cavity

• Deep cavity, poetically

• Deep gulf

• Deep-bottomed pit

• Deep, dark pit

• Grand Canyon e.g.

• Immeasurable cavity

• Immeasurable void

• It's immeasurably deep

• Profundity

• Really big cavity

• Unfathomable crevasse

• Vast gulf

• Wide gulf

• Wide gulf, poetically

• Yawning chasm

• Yawning chasm (var.)

• Yawning depth

• Yawning gulf

• Yawning gulf (Var.)

• A bottomless gulf or pit