"Nessun Dorma!" In other words, "No One Shall Sleep." That's the English-translated title of Puccini's most famous aria, sung by everybody from Luciano Pavarotti to Aretha Franklin, and it also suits Philadelphia's forthcoming opera schedule from late April into early May.

Four significant opera organizations in and around the city are opening five productions -- within days, hours, and, in some cases, a few blocks of one another.

It's a windfall for regular operagoers, no doubt. And for the "opera curious," the 12 days from April 27 to May 7 offer a high-density opportunity for a head-first immersion.

The big show in this month's accidental opera festival is Opera Philadelphia's production of Mozart's great servant-vs.-masters sex comedy, The Marriage of Figaro, April 28 through May 7 at the Academy of Music.

Babylonian rulers spew vocal fireworks in Rossini's Semiramide, part of Opera Delaware's Rossini Festival April 29-May 6. Also part of that festival's lineup: the comedy La Cenerentola (Cinderella).

Mozart melds fantasy and mysticism in The Magic Flute, opening April 29 at the Academy of Vocal Arts, with performances through May 9 in venues as far afield as Centennial Hall at Haverford and Central Bucks South High School in Warrington.

Puccini's La Rondine, April 27 and 29 at the Kimmel Center's Perelman Theater, brings together lush 20th-century harmonies and Viennese waltzes in a Curtis Opera Theater production under up-and-coming conductor Kensho Watanabe.

As an art form, opera may seem too impractically extravagant to have survived into the 21st century, but it is doing just fine anyway, and with a growing, younger audience. The vital and inventive Opera Philadelphia reports that 27 percent of its nonsubscription ticket buyers are between 25 and 34. Right now, president David Devan and his company are gearing up to present a new citywide opera festival, called o17, this fall. Stay tuned.

Not that Philadelphia was always a good opera town. Lots of talent has always passed through here, but it didn't always stay. Marriage of Figaro librettist Lorenzo da Ponte washed up here around 1805 when fleeing European creditors but reportedly wore out everybody's patience and quickly moved on.

Rather more recently, soprano Anna Moffo, who made La Rondine one of her signature roles, grew up in Wayne and didn't look back when she became one of the most glamorous opera stars of the 1960s. Even audiences at various points gave up on Philadelphia, considering opera-rich New York City is close by.

Now, audiences are migrating in reverse: Opera Philadelphia's fall festival last year had a 20 percent out-of-towner rate. Opera Delaware's spring festival last year drew 29 percent of its audience from beyond the Wilmington/Philadelphia area.

What audiences don't see is behind-the-scenes exhaustion. Example: Opera Philadelphia's forthcoming fall festival has a Berlin-imported, video-heavy tour-de-force production of The Magic Flute -- plus three world premieres of works that are not necessarily written yet. Last week, I encountered one of the company's resident composers, the tousle-haired 27-year-old David Hertzberg, as he was wrapping up his opera The Wake World for a Sept. 18 premiere. "I haven't slept in a year. Basically. More or less," he said.

Opera people can be as irrationally passionate as sports fans, though obviously for different reasons. The core appeal of opera is the power of the sung word, bolstered by the force of a full symphony orchestra, and vocalized by an artist whose every molecule is mobilized to make beautiful sounds that need no microphone. During the best moments, nothing stands between the composer's genius, the character's archetypal power, the singer's Olympic gold-medal art, and the audience, all fusing into a parallel reality that can be addictive.

And at its worst? Opera can be disastrously funny, with the great and the silly right next to each other.

The Magic Flute, for example. How could even the most forgiving millennial cope with the unintentional cheesiness of the first scene's dragon attack? Well, you look at it as symbolism in an opera littered with Masonic riddles worthy of The Da Vinci Code. You don't need to know what the code is, just that it's there. In fact, you don't have to understand more than 50 percent. Just take it in intuitively. The point isn't where you end up, but how you get there. This ain't the movies.

But when operatic choices are as numerous as movies -- as in the late-April, early-May whirlwind -- guidance is needed, though keep in mind, all such advice is guesswork. Once that curtain goes up in an art form with so many moving parts, nobody really knows what's going to happen. Were opera a well-oiled machine, it would be more like Broadway's Phantom of the Opera.

The Venues: The Academy of Music, opened in 1857, is an attraction unto itself with its 19th-century time-warp ornateness. Ditto for the similarly old-world 1871 Wilmington Grand Opera House. The Academy of Vocal Arts' headquarters, the tiny Helen Corning Warden Theater, is fun for its eccentricity -- it's an opera house in a townhouse -- though with dry acoustics. The best opera venue of all in Philadelphia is the Kimmel Center's 650-seat Perelman Theater: fine acoustics and intimate scale.

Old opera vs. new: Opera doesn't age according to chronology. Mozart's 1786 Figaro seems more modern than Rossini's 1823 Semiramide, partly because Mozart moves restlessly forward while Rossini freezes the moment and stays there for a while. La Rondine, the newest of the operas touching down this month (it's from 1917), might seem the creakiest dramaturgically. But how else are you going to hear its incredibly beautiful music? The Magic Flute (1791) exists outside any chronology because of the odd combination of vaudeville and symbolism (which assures that all of the opera's delightful elements come in threes).

Young professionals vs. seasoned professionals: The young opera professionals at Curtis and the Academy of Vocal Arts are often just a year or two away from debuts in major opera houses. Freshness is the upside; tentativeness can be a downside. Seasoned singers tend to be more accomplished, but also busier, and you sometimes hear the vocal mileage. Perhaps the main difference is operatic acting: In the evolution of a singer, the voice comes first, because without that there's nothing. Acting comes later.

Home vs. away: Convenience is overrated. Traveling for opera creates an extra sense of occasion. You meet it more than halfway. I haven't been to the Academy of Vocal Arts' Buck's County headquarters in years, and though the auditorium isn't ideal, the genteel wilderness experience up that way is something I adore. And without the usual dressing rooms, you're more likely to witness intermission arguments among the performers. And when back on stage, they're all friends again. Sort of.

The Marriage of Figaro

Opera Philadelphia, April 28-May 7 at the Academy of Music. Tickets: $19-269. Information: 215-732-8400 or www.operaphila.org.

The Magic Flute

Academy of Vocal Arts, April 29-May 9 at three locations, 1920 Spruce St., Central Bucks South High School in Warrington and Centennial Hall in the Haverford School. Tickets: $40-65. Information 215-735-1685 or www.avaopera.org.

Cenerentola and Semiramide

Opera Delaware, April 29-May 7, Grand Opera House, 818 N. Market St. Wilmington. Tickets: $29-99. Information: 302-442-7807 or www.operade.org.

La Rondine

Curtis Opera Theatre, April 27 and 29, Perelman Theater at the Kimmel Center. Tickets: $10-35. Information: 215-893-7902 or www.curtis.edu.