Oh, this one I know:
I'm sure the last thing you'll want to see during your travels is a
city's sewer system -- in fact, the less we know about what happens in
the dark and wet, the better. But browsing through the this gallery of shots from Tokyo's
underground, I think you'll agree there's something pretty interesting
going on down there. Looking like a cross between Japanese anime and
one of Ken Adam's classic set pieces for the James Bond films, I'm
surprised they don't offer tours. Then again, since photos don't transmit smell, maybe there is a reason.
UPDATE: Actually, they do offer tours.
The correspondent gets a big part of it wrong: it's NOT a sewer, it's a flood-control project, with the unlikely English-language monicker of "G-Cans Project". As such, the only smell on offer, I'm sure, is possibly that of cold damp concrete.
It's even been featured in a Land Rover TV commercial (requires Flash: click on "Range Rover Sport" when the page loads to see the Tokyo section) and print ad. And despite what's shown in the commercial, it's actually way up in the northern outskirts of Tokyo (actually, in Saitama prefecture), and nowhere near Shinjuku (where the commercial begins) or Yokohama (where it ends).
Tours are possible, it appears, but since they're conducted only in Japanese, they require you to bring someone to act as a translator (my guess is that they're worried about foreign visitors not understanding the safety rules). If you speak Japanese or know someone who does, call them at 048-747-0281 to make arrangements, which is something I ought to be doing myself someday.
Access from Tokyo:
The nearest train station seems to be Minami-Sakurai station on the Tobu Noda line, and there are a variety of ways to get there:
Method 1: From Tokyo Station, go to platform 3 and catch the Keihin-Tohoku line north to Omiya (25 minutes away). Transfer to the Tobu Noda line eastbound towards Kasukabe, Kashiwa, or Funabashi, and get off at Minami-Sakurai station (11 stations, 28 minutes away). Don't know what the bus lines are, so it's probably simplest to take a taxi from the station rather than walk for 2 kilometers.
Method 2: From Tokyo Station, go to platform 3 or 4 and catch either the Keihin-Tohoku or Yamanote line north to Akihabara (2 stops, 3 minutes). Exit and transfer to the Hibiya subway line going towards Kita-Senju station (6 stations, 12 minutes). Depending on the train you're on, either transfer at Kita-Senju station (if the train terminates there) or simply stay on it (if it continues) to the Tōbu Isesaki Line to Kasukabe (6-19 stations, depending on whether it's a local or express, about 28 minutes). Transfer at Kasukabe to the Tobu Noda line eastbound towards Kashiwa or Funabashi, and get off at Minami-Sakurai station (2 stops, 7 minutes away). Take a taxi.
Method 3: Use this website to figure whichever route works for you to reach Minami-Sakurai station. There, take a taxi.
南桜井 = Minami-Sakurai station
春日部市= Kasukabe, the name of the city
首都圏外郭放水路 = Official Japanese name for the project