This is one of the best things anyone interested in one of the most impressive engineering marvels ever can go and visit anywhere in the world. I cannot stress enough how good it is and how involved the tour gets (wearing waders to go waist deep in water to view the jet turbines used to pump water).
I strongly advise taking someone who can help translate Japanese with you as there's a huge amount of information to take in and it's a fantastic opportunity for anyone keen on photography as well.
Wikipedia: Metropolitan Area Outer Underground Discharge Channel - https://en.wikipedia.org/wiki/Metropolitan_Area_Outer_Underg...
https://news.ycombinator.com/item?id=19785044 - May 2019 (40 comments)
Tokyo Is Preparing for Floods ‘Beyond Anything We’ve Seen’ - https://www.nytimes.com/2017/10/06/climate/tokyo-floods.html - October 6th, 2017
https://news.ycombinator.com/item?id=15436943 - October 2017 (210 comments)
I strongly advise taking someone who can help translate Japanese with you as there's a huge amount of information to take in and it's a fantastic opportunity for anyone keen on photography as well.
You can go down, you can look at the place from one spot, bit you no longer can walk around.