It's a wall-painting from a pre-Roman tomb in Italy. It's just a pity so many people have rubbed at the painting and made a mess of the details, but she's clearly got a mouthful of one guy and is taking it from behind from another. And at the same time she's getting a spanking from both.
Now that's culture.
It does look slightly painful, I admit - personally I couldn't cope with bending over like that for long. But it'd be worth a try!
The article on this picture is here at the Spanking Art Wiki.