The weekend’s best in nightlife, music and art. For even more, check out Nightlife Agenda.

Major Lazer clearly tore it up at Coachella this year (pictured). Can DJ/producer Diplo and Co. re-create the dance hall magic Friday at the Mad Decent Block Party? (Jason Kempin/Getty Images for Coachella)

Friday: The bill for the Mad Decent Block Party, the daylong electronic music festival at Merriweather Post Pavilion,  reads like a who's who of bands you've never
heard of, including such acts as Major Lazer, SBTRKT, Anamanaguchi and Obeyah. But that's precisely why you should go. The Mad Decent record label is the brainchild of DJ/producer Diplo, who has one of the best ears in the business - he scouted
(and dated) M.I.A. We're curious, however, about how the blip-and-bleep set will fare breaking it down on a lawn in Columbia instead of a sweaty club at 2 a.m.

Saturday and Sunday:  How many Lego blocks can fit into 100,000 square feet of Dulles Expo Center floor space? You'll find out at BrickFair, the annual gathering of Lego builders from across the country for one great big family-friendly event. Look for interactive Lego sets, a hands-on playroom and Lego giveaways.

Saturday: The curtain rises on Signature Theatre's annual open house at noon and doesn't fall for 10 hours. Look for performances every 15 minutes across the theater's Shirlington campus, including a concert previewing the upcoming season; family cabarets; Q&A sessions with actors and directors; and the "Signature Idol" talent competition, which will be judged by artistic director Eric Schaeffer and Broadway vets. Signature Theatre, 4200 Campbell Ave., Arlington. 703-820-9771.

Saturday: After a two-year hiatus, the Washington Project for the Arts is wading back into the Capitol Skyline pool for the third SynchroSwim, a buoyant revival of the Esther Williams tradition, with an artistic twist. Four teams of artists and performers will dive in and perform aqueous, synchronized routines inspired by Antarctica, the wedding-industrial complex and more. The winner will be decided by a few esteemed judges, including Arena Stage artistic director Molly Smith and Arvind Manocha, the new Wolf Trap president.

Saturday: If the rumors about the Biebs - and, okay, copious video footage - are to be beliebed, the once adorable pop singer has transformed overnight from a boy wonder into a deliquent. The more tempered take on things? He's a 19-year-old with perhaps too much money and too willing an entourage (and too many drop-crotch pants, but that's a point for another day). Justin Bieber, who brings his "Believe" tour to Verizon Center on Saturday, is still a ferocious dancer and performer, and critical buzz reveals that this tour is full of the kind of whiz-bang action that makes fans think their money was well spent.

Sunday: The Mexican duo of Rodrigo Sanchez and Gabriela Quintero once played straightforward heavy metal, but when they left their home country for Dublin's vibrant busking scene, their choice of instrument - the nylon-stringed flamenco guitar - helped them forge what was arguably a new sound: flamenco metal. Their immense musicianship will be on display Sunday, when they perform in Strathmore's hallowed halls, and rumor has it that these master cover artists have been playing a version of Rage Against the Machine's "Killing in the Name."

Sunday: Throughout July, 50 bartenders across the area put their own spin on the Rickey, a refreshing summer cocktail born in Washington in the 1880s. On Sunday, it's time to reap the rewards. Eight finalists will prepare cocktails for judges and the public at the annual Rickey Month celebration at Jack Rose in Adams Morgan. Admission (a mere $35) includes unlimited cocktails, sandwiches and hors d'oeuvres.

Sunday: Before 11th Street was crowded with tacos, barbecue and wine bars, Wonderland was the only hangout for the 20-something residents of the neighborhood’s burgeoning group houses, offering cheap beer, no-cover DJ dance parties, jam sessions from hip local bands and a home to a thriving singles scene. The bar is throwing open its doors for its ninth anniversary, which means an all-night happy hour, food specials and music by Ian and Friends.

Through Aug. 11: After its second run at Arena Stage wraps this month, “One Night With Janis Joplin” and its pitch-perfect star, Mary Bridget Davies,are Broadway-bound (previews in New York begin in little more than a month, on Sept. 20). You've got just two weekends left to take in all the hippie, trippy fun.