The schedules were packed, there was only one day for sightseeing, and there wasn’t even enough money to provide Ed Solomon and Chris Matheson with per diem, but they did add some serious production with European locations.
The scenes filmed in Rome include the castle where they meet the girls, the fancy music room where they meet Beethoven, the square where they pick up Freud, the building where they find Socrates.
Being an independent movie, Bill and Ted’s Excellent Adventure had to save money where it could (for example, they filmed primarily in Arizona because it was less expensive than San Dimas, California), but there was one stretch where the production got an opportunity to pull a big blockbuster move and film for 10 days in Rome, Italy.