The inner sanctum of Hamburg's "Mile of Sin" looks as if it has been built to withstand a terrorist attack.
Barricades 3.6m high block off both ends of the notorious Herbertstrasse brothel and large signs warn visitors: "Under 18s and women - Verboten!" Adult males have to squeeze through narrow doglegs in the barriers just to get into the street.
Past the barricades, about a dozen prostitutes in full pornographic regalia sit perched in narrow shop windows on shiny swivel chairs covered with Playboy towels. They look like kinky Barbie dolls. Each one has a little glass porthole in her window to help her negotiate with clients.
Around 10pm last Tuesday, the only punters on Herbertstrasse were two Asian men enjoying a fit of the giggles. They walked up and stared transfixed at the street's most spectacular exhibit - a full-blown Teutonic dominatrix in knee-high black leather boots, matching corset and a mane of hair that covered surreal breasts. The dominatrix did not bat an eyelid or even look up. She was too engrossed in the novel she was reading.
Controlled and legal prostitution - at least the kind that made Hamburg's Reeperbahn famous and profitable for decades - is dying in what still rates as one of the world's most famous red light districts. And if the scene witnessed on what is reputed to be the area's most titillating street brothel was anything to go by, even its practitioners have become bored with the idea of organised sex for sale.
The message was driven home explicitly with the announcement that Hamburg's oldest brothel is to shut, having provided an uninterrupted service for its clients for the past 60 years.
Hotel Luxor is located in what could be described as the Reeperbahn's heart: a narrow side street called Grosse Freiheit or "Big Freedom". It is the street which was once home to the legendary Star Club that propelled the Beatles to fame.
Above the main entrance of Hotel Luxor an attempt is made to entice clients with a flickering neon sign that reads: "Pretty woman for happy nights." Upstairs the establishment is reminiscent of an Edwardian brothel: there is a small cocktail bar surrounded by acres of red plush and curtained-off niches.
In the middle of this sex emporium stands Waltraud Mehrer, a petite woman with bobbed blonde hair. She has been Hotel Luxor's madame for the past 21 years: "Yes, many people see our closing as a sad development," she said, "But you can't make money by offering real sex on the Reeperbahn any more. I blame it on internet sex, the noisy discos and dance clubs and the popularity of call girl services."
The brothel had its heyday in the 1970s when demand was so high that it stayed open 24 hours a day, seven days a week and employed 12 prostitutes. Now it employs four girls and is open four nights a week. The place will go on the market from April 1.
"The only things up and running in the sex trade are the table-dance clubs. The discos on the street have ruined our business," said Ms Mehrer.
The Luxor's demise is reflected in police statistics. In the 1980s, Hamburg St Pauli, the district in which the Reeperbahn is located, was home to more than 1000 prostitutes. Many plied their trade at the district's famous six-storey Eros centre brothel, which then counted as one of the biggest in Europe. The fear and spread of Aids forced the brothel to shut down in 1988.
Hamburg has fewer than 400 registered women on the game. Today, the Reeperbahn overflows with supermarkets, tacky discount sex shops offering such bizarre products as a beverage called "Cock a lada", transvestite clubs, cheap eateries and bars which give their teenage customers the chance to get drunk for as little as ¬5 ($9.65).
The surge in teenage binge drinking has been accompanied by an alarming increase in violent street crimes, with up to 50 incidents of actual or grievous bodily harm reported each weekend.
More than 43 per cent of the perpetrators are under 21. The police and city authorities have responded with CCTV surveillance cameras and, last year, they imposed a ban on weapons, including knives and baseball bats.
Just a few doors up from the doomed Hotel Luxor, drinkers still flock to Gretel and Alfons, a pub that the Beatles used to frequent virtually every night during their sojourn in Hamburg in the early 1960s.
Patti, the pub's barmaid, looked back nostalgically to the days of the Fab Four. "Back then this place was the centre of the pop music business," she said. "Now there are hardly any music clubs any more and the whole area is overrun at the weekends by teenagers who flock to the 99-cent bars and get smashed."
Her views were echoed by Siggi, the 72-year-old doorman at the Safari club opposite. The club is Hamburg's last "live" establishment and its acts include a rendition of Fred and Wilma Flintstone indulging in stone age sex on stage.
Siggi, who has worked at clubs on the Reeperbahn since 1951, said: "In the old days, there was no live striptease, only film of nice-looking girls naked from the waist up. The whole atmosphere was different."
Thirty years ago, the venues around Siggi's club included a dance bar/brothel equipped with table telephones which enabled customers to ring up any prostitute they fancied, a miniature circus with a ring, prancing horses and animals that did tricks and perhaps most novel: an act that involved women wrestling in mud with the front row of the audience protected by a large rubber sheet pulled up to the neck.
The Star Club, which attracted not only the Beatles but the likes of Cream, Chuck Berry and Ray Charles, closed its doors in 1969. The first attempts to cash in on the area's Beatles' legacy was made in 2006 when a Hamburg radio station and the city government announced plans for a Beatles Square. Two years on, the project has failed to materialise.
Critics blame Hamburg property developers such as Andreas Fraatz, the grandson of the former red light district "king", Willy Bartels, for the Reeperbahn's demise. Mr Fraatz reflects a trend that began in the 1990s when the city government began gentrifying sections of the St Pauli district. He is behind a development project that includes 300 flats for high-income earners and offices for a major advertising agency.
Few oppose Mr Fratz more vociferously that Karl-Hienz Bttrich-Scholz, an ex-Reeperbahn policeman and head of the St Pauli Preservation Society to which 200 of the district's businessmen belong. He is adamant the area should stick to its pornographic traditions.
"The Reeperbahn is the most important street in the world alongside 5th Avenue," he maintains. "International guests do not come to Hamburg for the seagulls, they come for the Herbertstrasse or to go to the Bums show."
Yet probably the most significant reason for the Reeperbahn's seemingly terminal decline lies 2km away on the opposite bank of the mud-brown River Elbe. The container port has more lights than the Reeperbahn and is busy around the clock all year. There are plans to dredge the Elbe to accommodate bigger, deep-draft container ships.
People like Siggi remember the 50s and early 60s when the streets of the Reeperbahn thronged with sailors because, back in those days, cargo ships took at least four or five days to unload, which allowed their crews a run ashore every night. "These days the turnaround on the container ships is so quick that the crews often don't even get off," said Siggi.
To remind visitors of what those good old days were like, Hamburg has resurrected one of the old, slow-to-unload cargo ships. The Cap San Diego is a beautiful freighter kept in immaculate condition as a museum ship and visited by thousands of tourists each year. To complete the picture, a handful or so have been known to spend the evening on the Reeperbahn - before it disappears completely.