Not sure why, but I've really been wanting to find this location that shows up in UM 45. It wasn't up on my page that lists genba shooting locations before heading off to Japan, and I didn't think to check to see if the spot was up yet while I was in Japan. (Or maybe I did, and it wasn't up yet? I know I hit the page to get directions to the sandwich spot -- which, it turns out, was used in episode 37 as well -- shiranakatta.)
At any rate, the address is up now. Turns out it's practically across the street from the feckin' JR Tachikawa station. head --> desk. I've been meaning to get out to Tachikawa for years now, since it shows up in Yakumo Tatsu. It's -- what? -- not even 30 minutes by express from Tokyo Station? So easy to get to, *whimper* The park where Mebius and Jack chat at is there as well. Which means this is probably landing on my personal list of Places To Go on the next trip.
For my reference, the address is: 東京都立川市曙町二丁目