Haarlem lies a few miles/km West of Amsterdam. It has a small red light district with around 38 windows / kamers (area indicated below). Most of these windows are within private areas so are hidden from public view. Just six windows are directly visible from the street. The largest private area is 't Poortje right beside Waalse Kerk with 20 internal rooms and an adult cinema (room with a big TV). In 2011 admission dropped from 6 Euros to 2 Euros. 't Steegje has six windows, four of which are inside. De Rode Lantaarn has another seven inside rooms.
The Waalse Kerk was built in the middle of the 15th century. The area / streets immediately around the Waalse Kerk are known as Begijnhof. This can be a little confusing when trying to find a particular address. Begijnhof derives it's name from the Beguines and Beghards. These were Roman Catholic religious communties that lived in the area.
Safety and advice. I found the area very safe and it seems to be in a nice neighbourhood. I am sure there are tourists that pass through or visit the church without even noticing the red lights. There is a single adult shop on St. Jansstraat but none of the other Amsterdam style attractions (apart from the windows of course). Thankfully as far as I could tell there are none of the beggars, drug dealers or other low life either.
Photography is not permitted in the 'internal' areas. When I started taking pictures of empty rooms in De Rode Lantaarn someone ran down from upstairs (there's CCTV every where) and told me not to. I pointed out there were no girls working at the time but was told that I still couldn't take photos. I returned later and sneakily grabbed the remaining pics and video I needed to complete this page. It did mean however that the video and some photos are of poor quality.
Getting there. Haarlem makes a good day trip from Amsterdam. Trains from Amsterdam Centraal station depart every few minutes from platform 1 or 2 and take around 17 minutes. The price is 7.40 Euros return (in November 2011).
Be sure to also check out the Grote Kerk (or St. Bavokerk) in Grote Markt. It's an impressive structure and well worth a visit even if you aren't normally into that kind of thing.