Cavegina 

A vagina with a width, depth, and volume such that it is often mistaken for a cave.

Ex. 1) Bob was delighted to have his first girlfriend, but when he got to 3rd base he found his arm swallowed by Lucy's immense Cavegina.

Ex. 2) Andre was known for his tree-trunk sized impregnator, but he met his match when a wild Cavegina appeared and swallowed it whole.

Cavegina by Lord Teapot March 18, 2013