De Wallen is the oldest part of Amsterdam: medieval lanes and small canals east of Dam Square, the city's first harbour district. Sex work here is legal, licensed and taxed, and it is done from ground-floor windows edged in red. In the middle of it stands the Oude Kerk, consecrated around 1306 and the oldest building in the city, with the windows glowing red around its churchyard. That collision is the district.
The Netherlands lifted its ban on brothels in 2000, bringing the trade under labour and health regulation rather than trying to end it. Cannabis is sold in permitted coffeeshops under a policy that tolerates the retail while the supply stays illegal, a contradiction the Dutch acknowledge. By daylight the quarter is a different place: quiet, genuinely pretty, some very good small canals, and the church open. After dark the lanes fill, and the city's long argument about what mass tourism has done here becomes visible on the pavement.