There are wide noodles, such as Kishimen (Aichi), Hoto (Yamanashi), and Dango soup (Oita), all over the country, but as far as I know, Gunma's specialty "Himokawa Udon" is the widest. You can have this in Ginza.
It is "Hanayama Udon Ginza Store" located in Ginza 3-chome, behind Kabukiza Theater. The main store is located in Tatebayashi City, Gunma Prefecture.
The first thing I ordered was the tempura of Joshu Maitake mushrooms. It seems that some ingenuity has been made to make it exclusively for tempura. It's crispy, fragrant and delicious!
And it is the appearance of the famous "Onihimogawa". It's 5cm wide. The chewy texture and the smooth throat were very delicious. Please drop in when you come to Ginza.