If you’re even remotely interested in modern dance, there’s only one place to be this weekend: at Zellerbach Hall in Berkeley, watching the Mark Morris Dance Group perform Morris’ two-and-a-half-hour masterwork, L’Allegro, il Penseroso ed il Moderato.

Choreographed by a 32-year-old Morris back in 1988, L’Allegro is heavy on artist cred. Based on olde-English poetry (John Milton’s) and classical music (a baroque score by Handel)? Check. Replete with full-on orchestra and even the medieval addition of chorale singing? Yes. Capped off by a long, philosophical Italian title (which means The Happy Man, the Pensive Man and the Moderate Man)? Done.

But this is not your grandmother’s Swan Lake. What you’ll see at Zellerbach is Morris’ signature festival of contrasts: two dozen strongly athletic, barefoot dancers dressed in flowing, balletic chiffon; choreography that is at once delicate yet modern, refined yet earthy; the structure and musicality of Balanchine layered with tongue-in-cheek slap-dashery and inventiveness (watch the women lift the men, for instance). The sum total is a work that helped blur the boundaries between ballet and modern dance, bringing both into the present instead of allowing one to linger in fairytale land while the other delved into unstructured angst as a reaction. Morris hasn’t brought L’Allegro to Cal Performances since 2003, and six years is a long time to wait. See you in Berkeley.