The Principality of Monaco, with its capital Monte Carlo, is much too small to have an airport. In fact the entire principality would fit in New York City's Central Park.
This episode takes place in July 1963.
This episode's title is based on a legend in Rome Italy. It is said that if one throws "three coins in Trevi fountain at the foot of the Spanish Steps" one is guaranteed to return to Rome. "Three Coins in a Fountain" is a 1954 film sharing its name with its theme song.