No sex, please, we're ultra-orthodox Jews – and it's just not kosher
The men stand at the front of the bus dressed in full-length, heavy black coats and wide-brimmed hats. The women sit at the back, huddled together to protect their dignity from physical contact or prying eyes. As I boarded the bus in the stifling 34C heat I realised living in Israel can at times feel like a bizarre cross between 1950s Ireland and 1980s South Africa.
Married couples have even been asked to produce their marriage licences if they want to sit together on the "kosher" buses.
All this in an effort to maintain the strict religious rules surrounding modesty, enforced not by law but by the ultra-orthodox Jewish men who stand guard.
Scuffles are sparked when someone tries to flout this segregation of the sexes, which is standard on a number of bus routes servicing religious communities. But in this heat I am in no mood to go toe-to-toe with a group of rotund, bearded religious fanatics and take my seat at the front with the other men.
Most secular Israelis see kosher buses as sexist and discriminatory, but the ultra-orthodox community here could care little what the outside world thinks.
"Are you Jew," I was asked by one after I turned down his offer of a blessing on a holy day. The moment the Hebrew word for "no" left my lips he turned his back and walked away. The ultra-orthodox treat outsiders with great suspicion and don't tend to mingle with gentiles.
But their desire for separation from the outside world is matched by strict segregation within their own community.
The women are not only kept apart from men on buses, but also in the synagogues, while walking the streets and on kosher beaches where each sex has their designated days to bathe.
And just as it once was in Ireland under the staunch guidance of the Catholic Church, sex before marriage is strictly forbidden. Hence most couples are clueless when it comes to canoodling on their wedding night.
But as I walked on the streets of Jerusalem recently there appeared to be a little twinkle in the eyes of those who follow the strict laws of the Old Testament. The question is, is this in anticipation of a new sex guide aimed at teaching the ultra-orthodox the "ins and outs" of married life before they tie the knot?
The birds and the bees is a taboo subject among the cosseted, God-fearing, orthodox Jews. So Dr David Ribner's The Newlywed's Guide to Physical Intimacy (pictured above) hopes to enlighten the sex lives of Judaism's most secretive and closed community and help make their time in the bedroom blossom from the outset.
"Sex is only appropriate within a marital context," says Dr Ribner. "So we wanted to give people a sense of not only where to put their sexual organs, but where to put their arms and legs."
The book begins with the basics and outlines the difference between the male and female body, but, to ensure not to offend, all illustrations are concealed in an envelope at the back of the book with an explicit warning.
The Fifty Shades of Grey phenomenon may have proved the Irish are no longer prudes when it comes to the sporty shenanigans carried on between the bed sheets, but the strict sex lives of the ultra-orthodox in Jerusalem would be unlikely even to make the Pope blush.
However, it is not just the sex lives of the Haredi (which in Hebrew means "trembling in the face of God") that are frozen in time.
Large families of eight or more children are still the norm thanks to the strict adherence to the Biblical commandment to "be fruitful and multiply".
And even though there are an estimated 1.3 million Haredi worldwide, most live apart from secular society, which they regard as intrinsically corrupt. Children are educated in strict religious schools and receive little or no sex education, while television, secular newspapers and visits to the cinema are forbidden, and use of the internet is treated with great suspicion.
Orthodox Judaism even forbids unmarried men and women from having any physical interaction, and some teenage boys are so worried about the consequences of masturbating they go so far as to tie their hands behind their backs.
While it is an urban myth that ultra-Orthodox Jews are so modest that couples have sex through a hole in a bedsheet, relations between the sexes are stringently policed, and arranged marriages are the norm.
Special classes that guide them through the very basics of male and female genitalia and "how a baby is made" are attended just weeks before they are married.
"In an Orthodox community, most people's first taste of sex will be within marriage, even down to hand touching and kissing," says Dr Ribner.
"So a manual that breaks down the inhibitions of asking questions and enables couples to get it right, is of great value. Especially because the knowledge about sex in these communities is very limited."
But while the book is set to be published in Hebrew in the coming weeks, very few bookshops in Jerusalem's religious neighbourhoods are likely to stock up on the sex manual for fear of offending customers.
So while the sexual revolution may have taken far longer than the swinging Sixties to set Irish bedrooms alight, it appears little is likely to change when it comes to the sex lives of the God-fearing uber-religious in Jerusalem.