cavernous (adj.)

• abysmal
• abyssal
• boat-shaped
• bottomless
• bowl-shaped
• commodious
• concave
• dish-shaped
• dished
• funnel-shaped
• gaping
• hollow
• incurved
• navicular
• retiring
• reverberant
• saucer-shaped
• scaphoid
• sepulchral
• soundless
• sunk
• sunken
• unfathomable
• unfathomed
• unsounded
• vast
• yawning