deep tongue spelunking

A severe type of cunnilingus (oral sex on a woman).

Deep tongue spelunking usually involves trying to get ones tongue as far into the vaginal cavity as possible.
This is usually done by tilting ones head back and almost inserting the lower jaw/chin.

Use with caution "DTS" has been known to cause severe neck injuries and may also lead to trout mouth if the receiver has not been properly identified.