BAYREUTH, Germany >> This small city is known throughout the world for its summertime Wagner festival, founded in 1876 by Richard Wagner himself. But long before the “Ring” cycle, Bayreuth had another operatic visionary.

Wilhelmine, Margravine of Brandenburg-Bayreuth, was the eldest daughter of King Frederick William I of Prussia, and the sister of Frederick the Great. An ambitious polymath who composed music, wrote verse and corresponded with Voltaire, she built Bayreuth’s intimate yet elaborate Margravial Opera House, one of the most outstanding surviving examples of Baroque theater architecture in Europe.

On Tuesday, the nearly 300-year-old opera house — a UNESCO World Heritage site since 2012 — reopens to the public after a six-year renovation that cost $36.6 million and returned its dazzling ornamental details, murals and trompe l’oeil effects to something approximating their original brilliance.

“Centimeter for centimeter, you can see that we got our money’s worth,” said Thomas Rainer of the Bavarian Palace Department, which oversaw the renovation, during a tour of the building last week.

In addition to the painstaking restoration and conservation of the theater’s ornately painted, gilded surfaces — which took some 70,000 hours of work and brought more lightness and brightness back to the interior — the proscenium has also been enlarged to its original dimensions, after having been reduced during an earlier renovation.

The chairs in the roughly 500-seat house have been replaced and can be adjusted according to performance requirements, and the lighting has been judiciously updated with LED bulbs that suggest the warm glow of candles. Behind the scenes, the stage machinery has been modernized, the temperature in the auditorium is now regulated, and the building’s ceiling has been freshly insulated.

“Today, Bayreuth is the cultural capital of Bavaria,” Markus Söder, the minister president of Bavaria, said before the gala opening of the theater on Thursday, addressing an invited audience that included Katharina Wagner, the artistic director of the Wagner festival and Richard Wagner’s great-granddaughter, and Christian Thielemann, that festival’s music director since 2015. Also in the crowd was Georg Friedrich, Prince of Prussia, the great-great-grandson of Wilhelm II, the last German emperor.

Built in 1748 from plans by Joseph Saint-Pierre — with the interior designed by Giuseppe Galli Bibiena, the leading theater architect of his day, and his son Carlo — the Margravial Opera House was inaugurated that September as part of the wedding festivities of Wilhelmine’s only child, Elisabeth Friederike Sophie, to Carl Eugen, Duke of Württemberg.

The building has remained in good condition largely because it was little used after Wilhelmine’s death in 1758. After Wagner’s plans for a festival in Munich devoted to his works fell through, he was entranced by the Margravial Opera House, but it was much too small for the epics he envisioned. (He ended up building a new theater, on a hill about a mile north.)

The rededication program on Thursday included a performance of an opera from not long before the opera house was built: Johann Adolf Hasse’s “Artaserse” (1730), in a postmodern staging by the Theaterakademie August Everding, a conservatory in Munich. The production, directed by Hungarian director Balazs Kovalik, drew parallels between Pietro Metastasio’s popular libretto about family intrigue at the ancient Persian court — it was set to music more than 90 times — and the story of Wilhelmine and her family.

In addition to the spirited and vocally resilient student cast, the production featured the distinguished German soprano Anja Silja in the speaking role of the Margravine. As Silja, still redoubtable at nearly 80, read passages from Wilhelmine’s letters and diaries, the characters around her shifted fluidly from Persian to Prussian.

Over the course of the evening, the production dramatized many of the defining events of the Margravine’s life, including her father’s cruelty; her love for her gay brother (offstage, Frederick the Great’s sexuality is a matter of historical debate); and the building of her opera house, which was represented by a miniature model onstage — suggesting the sort of mise-en-abyme effects the Bibienas were renowned for in their set designs.

Productions like “Artaserse” will continue to take place at the Margravial Opera House, but it will not become an active full-time theater. Conservation-based limits have been placed on how often the house can be used for performances, and none will be programmed during winter, since the comparatively frail wooden interior cannot withstand extreme temperatures. (Throughout the year, visitors will be able to watch a multimedia presentation and view the auditorium.)

Events scheduled for the coming months include the Berlin Philharmonic’s annual European Concert, a Chopin recital by Russian pianist Daniil Trifonov, and a Czech production of Monteverdi’s “L’Orfeo,” from 1607, which is commonly regarded as the first modern opera.

It’s easiest to imagine early operas here, rather than more common 19th-century works that require larger forces and benefit from bigger houses.

“Performing Wagner here,” Rainer said, in an understatement, “would be difficult.”

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