Contemplation of the body...as a cave

Staying attached to the cave,
covered heavily over,
a person sunk in confusion
is far from seclusion — 
for sensual pleasures
sensual desires
in the world
are not lightly let go.

Guhatthaka Sutta-The Cave of the Body
http://www.accesstoinsight.org/tipitaka/kn/snp/snp.4.02.than.html