A portal to another dimension

Kind of like the Mickey Mouse Club House, "cum inside, have fun inside"

In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vulva to the cervix. The outer vaginal opening is normally partly covered by a membrane called the hymen. At the deep end, the cervix (neck of the uterus) bulges into the vagina. The vagina allows for sexual intercourse and birth. It also channels menstrual flow (menses), which occurs in humans and closely related primates as part of the monthly menstrual cycle.

A portal in which a ritual called sex is held which brings a demon from another dimension into earth

The ritual requires a male and a female

Where penises go in, and babies come out.