Let's see... From Shinjuku Station take the Chuo Rapid (Orange train) to Kanda Station. Exit Kanda station for the 'Ginza' subway line. Take the Ginza line train going towards Ueno. Stay on that train until it reaches Asakusa. Some trains stop at Ueno, but I think that's only later in the evening hours. Asakusa is the last top on the Ginza line. Also, Minowa station is close as well, that's on on the Hibiya line. There's not an easy way to access the Hibiya line, except going to Ginza station and changing there. (At least from Shinjuku, that's one way to do it... after taking Chuo Rapid to Kanda) See the attached map. Blue circled area is Yoshiwara district. (吉原) Red circles are Asakusa and Minowa stations. (North and South, respectively.) You get on google and make a map to get to the Yoshiwara area. If I can think of better details, I'll post them later.