In ancient Rome, architect Lucius is renowned for his thermae bathhouses, but clients reject his ideas for being outdated. At home, his wife pressures him to have a baby due to financial struggles. When a friend brings Lucius to a public bathhouse to relax, he finds it too noisy. Seeking peace, he goes underwater and is whisked away into a mysterious tunnel. Emerging in modern Japan, Lucius is greeted by confused onlookers in a public bathhouse. The sudden change leaves him bewildered.