"Yuureitou" (The Phantom Tower) by Edogawa Ranpo. A story with many plot twists, with bits of murder mystery, bits of treasure hunting adventure, and bits of romance. It has many exciting elements typically found in Edogawa Ranpo's stories, such as hidden rooms and disguises. There are enough interesting bits that makes this book worth reading.
Though actually, this story wasn't originally written by Edogawa Ranpo. It's really a modernization of another "Yuureitou" by Kuroiwa Ruikou. That version is freely available online:
http://www.aozora.gr.jp/cards/000179/card943.html
One modernization feature that is immediately obvious is that the grammar used is closer to modern times. While 1937 is is still many years away from 21st century light novels, it's decidedly less archaic than Kuroiwa Ruikou's version, which was first published in 1899. All the character names have also been changed, presumably with the same modernization intent (female names like "Onatsu" have gone out of fashion).
Grammar changes aside, I find Ranpo's writing generally more detailed and dramatic. For example, in a later scene where the heroine's history is revealed, the new version had detailed passages about the mental state of the narrator, explaining why he hesitated before picking up artifacts of the past. In comparison, the old version had the narrator simply picking up the same artifact, and immediately turning it over to read the same history that was on the reverse side. On the other hand, there are details like the wordy puzzle detailing the entrance to the clock maze was mostly cut in the new version. Some details are gone from Ruikou's version, but for the most part, I prefer Ranpo's version.
Actually, Kuroiwa Ruikou's version wasn't the original either. The original is supposedly "A Woman in Grey" by Alice Muriel Williamson, published in 1898. The copyright should have long expired by now, but none of the online libraries have digitized it yet. Not sure if this version is any good.
Having already listed 3 versions of the same story here, the one that I would recommend is actually a completely different 4th version -- the manga version of "Yuureitou" by Nogizaka Tarou. There is a new set of character names yet again, because this time around, the plot is almost completely different from all novel versions besides some general themes. Basically, there are now lots of books with clock tower as a plot element that are worth reading.
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