At Theatertreffen, an annual celebration of the best in German-language performance, music plays a profound, and intelligent, role.HAMBURG, Germany — During the five and a half hours I spent immersed in “Die Ruhe” (“The Calm”), a performative installation that was one of the 10 productions selected for this year’s Theatertreffen, I put a live worm in my mouth, cut off a lock of my hair and held a giant African snail.I also participated in a group therapy session, during which a severe doctor pushed us to share our secrets and fears, and drank bitter mushroom tea (non-psychedelic, I hope), vodka and schnapps.Along with the other 34 ticket holders for that day’s performance in the Altona district of Hamburg, I had checked in as a prospective patient at a fictional facility for people exhausted by modern life.At once intimate and visionary, “Die Ruhe” was far and away the most unusual and daring title in the remarkable first live Theatertreffen since the start of the pandemic. After spending the past two years online, the festival, which celebrates the best in German, Austrian and Swiss theater, came roaring back to life with a wide-ranging and eclectic lineup that highlighted the creativity, resourcefulness and persistence of German-language theater in 2021.Originally staged by the Deutsches Schauspielhaus theater here, “Die Ruhe” was the brainchild of SIGNA, a Copenhagen-based performance collective led by the artist couple Signa and Arthur Köstler, which has specialized in large-scale, site-specific performance installations for the past two decades. SIGNA was previously invited to Theatertreffen, in 2008, with an eight-day performance held in a former rail yard in Berlin. This time around, the installation was too complicated to transfer to Berlin, where all the other Theatertreffen performances have taken place, so in a break with tradition, “Die Ruhe” has been mounted in the former post office in Hamburg where it was originally seen in November.With the other members of my small group, I was guided through a sinister sanitorium whose inhabitants — patients and doctors alike — seemed to have all suffered a psychological collapse. Upon entering the post office, we were welcomed to the institute by being asked to lie down on mattresses on the floor. Shortly afterward, we changed out of our clothing and into the institute’s baggy uniform of gray hoodies and sweatpants.Simon Steinhorst in “Die Ruhe,” which was staged in Hamburg.Erich GoldmannAs I was led with the group through dimly lit corridors and rooms — including a simulated forest filled with damp earth and dry leaves — by a fragile and haunted guide, Aurel, it became clear that the institute was the center of a threatening and shamanistic sect. Over the multiple floors of the post office, SIGNA and its large cast (there’s an almost even number of paying participants and institute members) formulated a holistic worldview for the cultlike institute, complete with an origin story and a rigid creed that its adherents, even the mild-mannered Aurel, were fanatically devoted to: a vision of Edenic return symbolized by becoming one with the forest.Aesthetically, this stylishly designed immersive experience seemed to take inspiration from movies: from recent films of dystopian horror, including Yorgos Lanthimos’s “The Lobster” and Ari Aster’s “Midsommer,” as well as Stanley Kubrick and David Lynch, masters of atmospheric dread. As a marathon plunge into a complex and intricate world, “Die Ruhe” resembled another recent and more infamous project: the scientific institute DAU, devised by the Russian filmmaker Ilya Khrzhanovsky in Kharkiv, Ukraine, between 2009 and 2011, which was recreated in Paris in 2019. Like that controversial performance, “Die Ruhe” contained deeply unsettling elements: a strong, pervasive atmosphere of menace, as well as a demanding (and at times exhausting) format that forced the viewer-participant into disturbingly close confrontations with cruelty, manipulation and violence.Back in Berlin, none of the other Theatertreffen shows I saw came close to “Die Ruhe” in sustained intensity and startling originality, but the productions I caught were of a consistently high caliber, and formally innovative.A scene in Claudia Bauer’s “humanistää!,” an exploration of texts by the experimental Austrian writer Ernst Jandl.Nikolaus Ostermann/Volkstheater One of the lineup’s most striking features was how profoundly, and intelligently, musical many of the shows were. In several of the best plays, live music played a fundamental role in generating a distinctive aesthetic as well as meaning. In thinking so musically about theatrical practice, it seemed that many directors at the festival were pushing against the limits of language.From the hits by Britney Spears and Meat Loaf crooned by the cast of Christopher Rüping’s “Das neue Leben — where do we go from here,” to Barbara Morgenstern’s vast and haunting original score for Helgard Haug’s “All right. Good night,” a hypnotic and mostly wordless production about the 2014 Malaysia Airlines disaster, this Theatertreffen seemed to insist on the primacy of music both to conjure and to enrich intellectual and emotional states.The single most astonishing show on a traditional stage was Claudia Bauer’s “humanistää!,” a surreal and dazzlingly inventive exploration of poetic and dramatic texts by the experimental Austrian writer Ernst Jandl.Bauer is one of Germany’s leading directors, and she created this breathtaking theatrical immersion in Jandl’s playful linguistic cosmos at the Volkstheater in the poet’s native Vienna, which is where I caught the production several months ago. (It remains in the company’s repertoire and is also available to stream on Theatertreffen’s website until September.)In “humanistää!,” 10 works by Jandl attain new vitality through conventional monologues, onstage projections and elaborate vocal performances reminiscent of Jandl’s radio plays. Bauer complements the torrent of highly musical texts with startling visuals and energetic performances that beautifully match the rhythm of Jandl’s sound poems. Eight actors perform vigorous and highly choreographed pantomimes and dances amid Patricia Talacko’s shape-shifting set, which is spectacularly lit by Paul Grilj. Throughout, Peer Baierlein’s propulsive music, performed live, accompanies the performers as both their bodies and their voices twist through Jandl’s linguistic games.Lindy Larsson in Yael Ronen’s “Slippery Slope,” an English-language musical about cancel culture.Ute LangkafelText and music combine in a much more straightforward, yet no less riotous, way in the Israeli director Yael Ronen’s “Slippery Slope,” an English-language musical about cancel culture with infectious songs and foul-mouthed lyrics by the singer-songwriter Shlomi Shaban. When it premiered at the Maxim Gorki Theater in Berlin in November, it was an immediate cult sensation. It’s not hard to see why.The plot, about a disgraced Swedish pop star (Lindy Larsson) trying to stage a comeback, and his protégé (Riah Knight), whose meteoric rise is inversely proportional to her mentor’s fall, is both sordid and deliriously enjoyable.What’s more, the five actors in the show can actually sing — a true rarity at German theaters — and they belt out Shaban’s rousing and cheeky numbers with gusto. For perhaps the first time I can remember, Broadway-caliber musical entertainment has come to a German dramatic stage. (It’s the only production from a Berlin repertory theater at the festival.)Cultural appropriation, political correctness, #MeToo debates and social media trolling are gently skewered in a production that is eye-popping and outrageously glam. At the same time, everything is so loopy and chock-full of schlock that there’s little danger of anyone’s taking offense at this vulgar and punchy musical burlesque. Although its themes are urgently contemporary, “Slippery Slope” handles them with a lightness and wit that are rare in theaters here. I’m glad that the Theatertreffen jury, a high-minded bunch of tastemakers if there ever was one, selected it alongside the festival’s more straight-faced entries. It’s a sign of their belief in theater’s ability to startle, to provoke and, yes, to entertain.TheatertreffenThrough May 22 at various theaters in Berlin, and at the Paketpostamt in Hamburg; berlinerfestspiele.de. More