In Rome in the year 128 AD, a Roman named Lucius Modestus is having trouble coming up with ideas for architecture. While contemplating in a bathhouse, he discovers a strange drain than sends him to a bathhouse in Modern Japan.
Lucius is commissioned by a sickly man to build an outdoor bath near Vesuvius. While inspecting a heated well, Lucius is once again sent to modern Japan, this time winding up in a hot spring.
As Lucius hears requests about private baths at home, he once again ends up in modern Japan and learn about more modern conveniences, specifically a bathtub.
Lucius has a strong urge to use the toilet, however he is summoned by the Emperor Hadrian and has to bear it. He is sent once again to modern Japan, this time in a toilet-showroom.