Animatronio mentioned a fountain. That's a statue of Neptune, god of water. The number of points on him trident is three, or trey. The "u" in his name is written like "v". Trey, "v". Trevi! It's the Trevi Fountain. There can be no question!
This except instead of going directly through that thought process, one character will say, "I've got it! Follow me!" And the chapter ends, followed by a chapter from the pov of every other character who isn't involved in that discovery.