A red light district - Idioms by The Free Dictionary
red-light district (redirected from a red light district)
An area in a city containing brothels and other businesses related to activities that are typically illegal elsewhere. If you patronize the red-light district, you're essentially subsidizing the sex trade.
red-light district an area of a city or town containing many brothels, strip clubs, and other sex businesses.
the red-ˈlight district the part of a city where prostitutes work and sex shops are found: I got lost and found myself in the red-light district all alone!