cavernous

Short definition from Wiktionary

Adjective

1. 1
   Resembling a cavern in size, shape, or atmosphere.
2. 2
   Resembling a cavern in size, shape, or atmosphere: Giving the impression of vast, dark depths.
3. 3
   Having many caverns: Composed largely of vascular sinuses and capable of dilating with blood to bring about the erection of a body part.
4. 4
   Having many caverns: Having cavities.