I find traveling by train soooo relaxing, though I guess some countries don't really have a train culture.
If you travel to Japan now, you realize that trains are still an important part of Japan as a country, not just as a vital lifeline, but also as part of the culture. This is also reflected in Japanese mystery fiction, where trains are a very common sight, sometimes revolving around iron-clad alibis that make brilliant use of time schedules, sometimes focusing on other related elements ranging from ekiben (lunch boxes with local specialties), the layout of stations, the morning rush and much more than I can name. However, Yamamoto Kouji, who works at a railway company, however interestingly doesn't write about the modern day railway in Japan, but about its past with The Detective of Meiji Period Railway. Most of Yamamoto's novels are mystery stories in a historical setting (Edo period) that predate railways, but with this novel, he decided to look at the earliest days of the Japanese railway network, which is a highly original theme.
If you're into history especially, this book is really interesting. It genuinely presents the Japanese railway network as the focal theme of the book, and looks at it from various angles. Inoue for example suspects there's a political motive behind the sabotaging of the project, putting the railway network in a 'big history' context about the various parties involved with the Meiji Restoration. At the same time, the book also looks at the railway as an element that juxtaposes Japan and the West, as something that Japan needs to master in order to become a player on the international scene, while foreign powers wish to use the railway to assert their superiority over Japan. And as the investigation continues, we also look at the railway at a smaller level, focusing on people who once earned a living by transporting people and goods across water and who are now losing their jobs, to people who are now able to travel across Japan more swiftly which can sometimes even save lives. The manner in which The Detective of Meiji Period Railway presents trains and a railway network as something new in society, all the changes it brings and how that can lead to crime is highly entertaining. It does help if you have rudimentary knowledge about political/sociological/economical circumstances around that time for the details, but I think that even without that, you can enjoy this as a historical mystery about trains.
The core mystery plot feels a bit like a Holmesian adventure, which is fitting considering the time period of course. Don't expect a Queen-like densely clewed puzzler, or mystifying impossible situations: it's more about Kusakabe and Onodera poking around, stumbling upon some fact that may or may not be relevant and other incidents occuring that push the story forward. A lot happens between the first and final pages of this book, but not everything is actually directly connected to the problem of the sabotage and like a lot of Holmes' adventures, the story feels a bit 'open', making it seem like anyone could've done it, and that you're just there for the ride to see what did actually happen. Ultimately, an interesting plot is revealed and we see some events connecting to others in unexpected ways, but I think the merits of this book as a mystery lie more on the historical setting and its focus on railways, than on specifically the manner in which this story has been plotted.
Strangely enough, the book does feel a bit... cramped? The story is about railways, but most of the story is set just around the tunneling site, and the town nearby, so there's not really a lot of travelling by train done here, and when it occurs, it's never actually shown in detail. This is really a railway mystery, not a train mystery. Most of the important events also play outside or around the half-finished tunnel, so in that regards, it feels more open than you'd expect from a railway mystery (not just inside a train), but at the same, it's less about the connection between various/multiple locations.
So if the topic of the history of the railway in Japan appeals to you, Kaika Tetsudou Tantei (The Detective of Meiji Period Railway) is a must-read, as it brings a rather fascinating story that really focuses on what the railway really means for a modernizing society and uses those changes to bring an interesting tale of mystery. In terms of writing, it's perhaps closer to the adventure-like stories of Sherlock Holmes, so don't expect minute-perfect alibi tricks that use twenty train lines to make the impossible possible or super complex plotting, but it keeps the reader entertained from the start with lots of incidents happening and also a surprisingly broad (economical/sociological/political) look at the Japanese railways.