A bit of a historic one as the line in question is now in two separate sections, but I think the 112km line between Takasaki and Nagano could be an interesting thing for TSW. The line needs to negotiate the steep (6.67%) Usei Pass so all trains needed banking and braking assistance from the specialist EF63 locos, operation of which could be a fun experience and a way to break up a journey. Unfortunately the Usei pass section closed in 1997 - replaced by a Long and slightly less steep Shinkansen tunnel. The sections either side are still in use. Stock EF63 489 Series Some details from Wiki https://en.wikipedia.org/wiki/Usui_Pass https://en.wikipedia.org/wiki/Shin'etsu_Main_Line
