"People lived there, in cardboard boxes; there were always 100 to 150 people," said the 36-year-old, pointing to a tunnel under a shopping mall near the main station of Utrecht, in the central Netherlands, during a recent preview of the inaugural tour on Sunday.
With four other ex-street dwellers and drug addicts, Diana has completed a sponsored course to present a unique, 90-minute tour of the city's darker side.
Entitled "Utrecht Underground", it is part of a rehabilitation project run by mental health care organisation Altrecht. A ticket costs five euros.
"One could find anything there: cocaine, heroin, ecstacy, prostitution, stolen goods," said the woman with the long dyed-blonde hair and carefully lacquered nails, who despite obvious pride in her new calling declined to give her full name.
Nowadays, the entry to the tunnel is barred.
"How it stank," Diana recalled. "There were syringes lying around, people urinated everywhere. Twice a day, the municipal services came with a water truck to spray the tunnel. If you didn't escape in time, you got completely drenched."
It was in this tunnel that Diana, dragged into this way of life by a drug-using boyfriend, spent much of her nights in 2002 and 2003. "But I never slept at night; it was too dangerous! I would try to get some sleep at the day centre," she explained.
She also used to sell sex to support her 400 to 500-euros-a-day cocaine habit.
"It is still an every-day battle," she said.
"Any former drug addict who says that they will never touch the stuff again is a liar."
Diana led her audience to a bridge under which she used to take refuge from the rain.
Further down the street, at a former walk-in "users' area" set up for addicts by the city, she showed her audience around a room previously set aside for people to inject themselves with heroin using clean, sponsored syringes.
The tour group then enjoyed a coffee break in the nearby common room, rubbing shoulders with the homeless who visit the building in its new guise as a temporary employment agency for the destitute.
"I do these tours because I think it is important for people to see that it is not all bad, that there is a lot of support, that things have become much better and that Utrecht has been cleaned up," said Diana.
All guides have access to a special coach for when "contact with the old world makes us feel like using drugs again".
The city says it has seen an 80 percent decline in homeless people in nine years, down to 200 from as much as 1,200 in 2000, according to Altrecht. Many street dwellers also have psychological problems and drug habits.
In 2001, the police joined with social welfare and psychiatric organisations to tackle the phenomenon and related crime problems -- actively seeking out the homeless to lead them to help.
The authorities also erected nine hostels, with a total of 200 rooms, each with its own bathroom. They claim that the rhythm of living in such relative comfort has incentivised many beneficiaries to start a new life.
Further down the street, Diana ran into a former acquaintance exiting Utrecht's last remaining "users' area". They embraced and laughed together.
"He is back on the drugs, but he doesn't look too bad just yet," she later confided.
Since getting off the streets herself, Diana has been living in shelters and doing volunteer work. She plans to move into her own apartment next year.
Diana, who will be paid 11.50 euros per guided tour, said she never carries much money with her in case she may feel a cocaine urge.
"If I were to ever win the lottery, I would die."