The story follows an ancient Roman architect named Lucius, who is having trouble coming up with ideas. One day, he discovers a hidden tunnel underneath a spa that leads him to a modern Japanese bath house. Inspired by the innovations found there, he creates his own spa, Roma Thermae, bringing the modern ideas to his time.
Each subsequent chapter follows Lucius facing some sort of a problem, just to be swept to Japan once again. He visits modern bath houses, personal baths, waterparks, fertility festivals, and even zoos. There, he always happens to find the inspiration to solve the exact problem he has been tasked with.
