Venusberg
Haven't we all been there? That is Laurence Coe's Venus and Tannhauser, circa 1896, up above. Eden, Arcadia, Cockaigne, the Holy Grail legends, Utopia, Shangri-La, the Venusberg, etc.; the mystery is that no one knows where any of them are.
Below is Tannhäuser in the Venusberg by pre-Raphaelite painter John Collier from 1901 (also see his Lady Godiva and Lilith). The basic storyline is that a mortal man is seduced by a fairy, in this case Venus, who lures him to her underworld fairyland, but then, after way too much sex, he becomes homesick (c.f. Homer's Odyssey). He is allowed to return home, and do penance in Rome (he's rejected), and he is not happy. In the end he returns to fairyland, and he is probably doomed to stay there...
There are several real Venusbergs today in Germany, one of which was among the thousands of labor camps created by the Nazis. But, obviously, the most famous use of the myth is Wagner's opera Tannhäuser — or, to use his complete title, Tannhäuser und der Sängerkrieg auf Wartburg (Tannhäuser and the Singers’ Contest on the Wartburg), meaning the Venusberg is somewhere around the Wartburg?
Do you believe that music can be highly sexualized? If you do, could it be considered "decadent" as well? 19th century opera goers like Baudelaire certainly believed it and many were scandalized (and thrilled) by it, although today it all seems a little hard to believe... Did Pierre Auguste Cot see/hear the opera? His painting below is often used to promote performances of Tannhäuser these days, so maybe he did.