Elektra, R. Strauss

Les Troyens, Berlioz

Les Troyens, Berlioz & Dido and Aeneas, Purcell

Mussorgsky, Boris Godunov

Die Tote Stadt, Korngold

Death in Venice - Britten

Giuseppe Verdi's opera Rigoletto is set in Mantua.

Nixon in China by J Adams. Act II Scene I. Visited by Pat Nixon. Sings aria in the Gate of Longevity and Goodwill

Towards the end of the 12th century, a literary court developed at Wartburg castle, attracted by Landgrave Hermann I, who surrounded himself with poets and musicians. The poetry of Walther von der Vogelweide describes the brilliant society life which gave rise to the episode of the singers' tourney at Wartburg Castle, a romanticized version of which inspired Richard Wagner's opera, Tannhäuser. (AB ev)

Verdi's Don Carlos takes place at the Aljaferia palace in Zaragoza.

Tosca - Puccini, The Coronation of Poppea - Monteverdi, The Clemency of Titus - Mozart, Rape of Lucretia - Britten

Act III of Giuseppe Verdi's Ernani is set in the tomb of Charlemagne (wiki)

Maria Stuarda, Donizetti

Turandot, Puccini

Romeo and Juliette, Gounaud

Das Rheingold, Wagner

Anna Bolena, Donizetti

"The Adventures of Mr Brouček" (1920) by Leos Janacek from the books by Svatopluk Čech. "Excursion to the Moon" commences "On a moonlit night in 1888, Mr. Brouček stumbles down Vikarka street after a drinking binge at the Hradčany tavern (Vikarka Inn").....". "Excursion to the 15th century" is also set in Staroměstské náměstí (Old town sq). There is today an inn in Vikarka St called "Vikarka Inn" which possesses "a Mr Brouček's Cellar" and "the oldest Romanesque wall at the Prague Castle" but whether that is the inn used by Čech and Janacek isn't totally clear!
See vikarka.cz

Torri Anunziata (Poppea's Villa) in The Coronation of Poppea by Monteverdi.

La Boheme (Quartier Latin)

Hamlet (A. Thomas)

Mussorgsky, Boris Godunov

The Italian Girl in Algiers, Rossini

Nixon in China by J Adams. Act II Scene I. Ming tombs visited by Pat Nixon. Sings aria next to Elephant in Avenue of Stone Figure

Saint Francois d'Assise by Messiaen (1983) Tableau 6 - Hermitage of the Carceri Tableau 8 - Church of the Porziuncola

Aida, Verdi