(CNN) -- To create the perfect travel itinerary, you can consider any number of factors such as scenery, culture or accommodations. Tony Perrottet chose sex.
Fascinated by secret stories and "perverse relics," the historian set out on his own unique version of the European Grand Tour -- a lengthy trip that was once a rite of passage for wealthy young men.
The journey was meant to broaden one's horizons, but sex was often part of the deal, Perrottet found.
"They're very intertwined, sex and travel," he said.
"You didn't just want to go to Rome to see the Colosseum. You didn't go to Paris just to have a look at the Eiffel Tower or the Seine. There was a sense of sexual liberation in these places."
So with his wife and two young kids in tow, Perrottet traveled to see some of the salacious spots that are now part of history.
He chronicles his trip in his new book "The Sinner's Grand Tour: A Journey Through the Historical Underbelly of Europe."
Here are five destinations on Perrottet's itinerary.
Southern France is famous for its wine, cheese, lavender and the good life, but this picturesque village in Provence also offers visitors a taste of the infamous.
The Marquis de Sade, whose sexual proclivities and ghastly novels inspired the term "sadism," made Lacoste his home in the late 1700s.
Sade's chateau still looms over the village but -- in a strange twist -- now belongs to French fashion designer Pierre Cardin, who stages an arts festival on the grounds each summer. (This year's Festival de Lacoste is scheduled to begin on July 15.)
A striking bronze sculpture of the marquis greets visitors who flock to the castle.
"Because of (Sade's) presence there, this whole village has always had this strange attraction for people over the centuries," Perrottet said.
But the tourists don't look creepy, he insisted.
"No, no. The locals were worried that it was going to turn into a pilgrimage place for bondage freaks ... but it's quite refined," Perrottet said.
"The tourists who go there tend to be the wealthier tourists from Paris and the Riviera who are attracted to Cardin's arts festival."
The "Sade name brand" is big in Lacoste these days, Perrottet observed, with visitors sipping espresso in the Cafe de Sade, shopping for local gourmet foods at Le Moulin de Sade gift store, and drinking Marquis de Sade wine, which Perrottet hesitantly sampled.
"It's very daunting because you think it's going to give you some shocking headache, but it's actually not bad."
Paris of the Belle Epoque
To explore the City of Light's "Beautiful Age" (from 1880 to 1914), Perrottet chose a unique guidebook: an 1883 prostitute guide, which featured detailed descriptions of the women and their addresses.
Also included: a list of the city's best luxury bordellos of the time.
"They were the most famous of all because of the sheer amount of wealth and money that was put into them," Perrottet said.
Some were "fantasy brothels" with elaborate themed rooms decorated so that their wealthy clients could imagine they were transported to the Renaissance, a pirate ship, ancient Rome and so on.
The best-known of these was Le Chabanais, near the Louvre, Perrottet said. Today, it's an office building with an antique facade that offers little hint of its unusual history. The interiors of the rooms were stripped and sold off after World War II, but the original marble staircase remains in the foyer, the author said.
His most memorable find on the trip was a "sex chair" said to have been commissioned in the 1890s by a future British monarch and kept at Le Chabanais.
The contraption, described as a cross between a sleigh and a gynecological chair, allowed the obese royal to have sex without crushing his partner, Perrottet said. Today, it sits in a Paris warehouse.
YouTube: Watch Perrottet talk about his quest to find the chair
The romantic home city of Giacomo Casanova -- whose memoir describes his seduction of 122 women -- has only one official memorial dedicated to the legendary lover.
But his spirit looms large, Perrottet said.
"Casanova is this mythic figure ... the ultimate symbol of the 18th century in Venice, which was the most voluptuous and sensual and decadent time in Venetian history," Perrottet said.
As part of his visit, the author crossed the Ponte delle Tette (politely translated as the Bridge of Breasts), where prostitutes once congregated; located the original door of an 18th century brothel; and rented a former casino, similar to one of Venice's once-secretive apartments that Casanova used for his trysts.
But the highlight of Perrottet's trip was going on the Secret Itinerary in the Doge's Palace -- a special unadvertised tour that takes visitors to the rooftop cells where Casanova was imprisoned in 1755 and ultimately escaped.
"It's great fun, because you go there and they literally open a secret panel in the wall and you go through while everyone else is just looking on in a sort of envy and irritation," Perrottet said.
"When you wander around there, you can actually follow the route that he took out. ... You get a sense of him as a real person," Perrottet said.
In 1308, the Inquisition visited this small village in the Pyrenees Mountains in search of heretics. They found lots of sexual intrigue instead.
The whole population was arrested and interviewed in great detail, so the surviving documents offer an intimate look at the everyday lives of ordinary people in the Middle Ages, Perrottet said.
Their love lives proved to be especially interesting.
"It's an extraordinary record -- an extraordinary soap opera, basically -- where these dozens of lusty shepherds and adulterous wives and horny farm hands recount their various adventures and ups and downs in this tiny village," Perrottet said.
"They're jumping in and out of each other's beds. Premarital sex is standard, illegitimate children are running around, ... people are running off with one another's wives."
Today, only about 40 people still live in the village, Perrottet estimated, though the population gets a boost during vacation season in the summer.
"It's an extremely dramatic landscape," he said. "It's a wonderful place to visit."
Stufetta del Bibbiena, the Vatican
Perrottet calls this "the most secret corner of the Secret City."
And he is here to confirm it's real: a bathroom in the papal apartments painted with erotic images by the Renaissance master Raphael.
Seeing the Stufetta del Bibbiena took exhaustive research, a flurry of e-mails, and tense interviews with Vatican officials.
"To this day, I'm not entirely sure why they let me in, but they did," Perrottet said, speculating all the intrigue raised by the author of "The Da Vinci Code" may have officials leery of creating more rumors.
"On a certain level, they're trying to open up certain parts of the Vatican to stop the Dan Brown fantasies of what's lying in there."
Just getting in the front gates of the Vatican was exciting, Perrottet said, something most visitors never get to do. (He was able to secure a pass because of his credentials as a scholar.)
Swiss Guards escorted him into the papal apartments, where he had 10 minutes to examine the Stufetta.
The two dozen images painted in 1516 -- which feature the goddess Venus in various poses with Cupid -- aren't shocking by modern pornographic standards, but they are provocative and were meant to be erotic, Perrottet said.
The fact that they're inside the Vatican makes them "100 times more powerful," he added. Today, the room sits empty, Perrottet said.