Epic shows: Never mind the quality, feel the length

It looks set to be a summer of endurance – and we aren't just talking about Olympic athletes. If you're heading to a theatre or opera house any time soon, you might well be letting yourself in for the long haul. Artworks are going epic.

One of the most celebrated opened on Friday: Einstein on the Beach, by composer Philip Glass and director Robert Wilson, is a rarely performed experimental opera from 1976.

There's no story. The score is flickeringly repetitive. The lyrics often consist of counting. And it's five hours long. With no intervals. You are free to come and go, but it doesn't feel that easy to "'scuse me" past rows of people concentrating on its incredibly intense, meditative quality.

Well, maybe not everyone's so swept along: the first crack after a mere 45 minutes. But then there are "technical difficulties": house lights up, all into the foyer. The relief is palpable, streaming off audience members gasping towards the bar.

I join friends; a bottle is opened, picnic eaten. When we're finally told to return to our seats, they're still singing numbers.

At 9.30pm, my row starts to empty. At 10.45pm I can see people taking Glass at his word and having a nap. Time becomes slippery: sometimes it flies by, sometimes it's like waiting for a five-hour flight to finish. On stage, a clock goes backwards: I know the feeling...

Einstein on the Beach is at the Barbican (barbican.org.uk) to 13 May

The Hobbit

Well, after The Lord of the Rings – running time: 557 minutes – you didn't expect The Hobbit to be a brisk 90-minute romp, did you? This adaptation of J R R Tolkein's children's book will be released over two films, out this year and in 2013. While the full length isn't yet known, given that they're also directed by Peter Jackson, you can expect a good five or six hours. Fantasy fans will be gleeful at the epic potential for a geek-out: back-to-back hobbitathons seem inevitable. Gird your loins for hours of Elvish, Orcs, and flowing beards. And please, don't even mention the extended versions...

Part one released 14 December

Hotel Medea

Pack your pyjamas: from midnight till dawn, you're to visit this most sinister of hotels. An immersive theatrical experience from Zecora Ura makes the audience part of a promenade performance retelling the Greek myth of Medea (the one who kills her kids to get revenge on her husband). The three-part drama lurches from a Brazilian disco to a twisted game of hide and seek, and ends with breakfast as the sun rises. All that tragedy is bound to make one peckish, after all.

Hayward Gallery (southbankcentre.co.uk), 20 Jul to 11 Aug

Gatz

This stage show is not just based on F Scott Fitzgerald's The Great Gatsby – it keeps every single word of the novel. an office worker picks up a copy and starts to read it out. Almost imperceptibly, his colleagues become part of the story and the fiction comes to life. Managing to be both the ultimate "faithful" adaptation and an inventive theatrical event, Gatz is performed by Elevator Repair Service and arrives in London trailing glowing reviews. It probably helps that you get ample breaks.

Noël Coward Theatre, as part of LIFT 212 (gatzlondon.com), 8 Jun to 15 Jul

The Ring Cycle

Staging the whole of Wagner's Ring Cycle is a fittingly grandiose project for the Royal Opera House's Olympic programme: starring Bryn Terfel, it comprises four operas, over four nights, kicking off with Das Rheingold (a breezy 2hrs 40mins). This is followed by Die Walküre (5hrs 50mins), Siegfried (6hrs) and finally Götterdämmerung (get comfy: it lasts 6hrs 30mins). A total of... 20hrs 20mins. You could fly to Beijing and back in that time - and it would cost you considerably less. A ticket for the full cycle, in the best seats, costs £1,000.

The Royal Opera House (roh.org.uk), 24 Sep to 2 Nov

Improvathon

An Olympic display of endurance: no script, no breaks (in the performance at least), no sleep for the actors. It's an entirely improvised soap opera, running continuously for two days, and performed by a core company of 25 expert improvisers, plus 25 guest performers. The audience doesn't have to stay for the duration: you can just buy event passes, for a two-hour slot (or seven) at any time of day or night. The theme is – what else? – the Olympics. You can expect this to be one of the more anarchic takes on it available this summer.

Hoxton Hall (hoxtonhall.co.uk), 11 May to 13 May