Entering Ai Weiwei's studio in Berlin is like descending into Hades. A black door on the site of an old brewery opens to reveal a cramped stone staircase that plunges underground, disappearing into gloom. This sepulchral passageway deposits visitors in a small, artificially lit brick chamber.Inside this dim room, ferocious beasts - actually, abstract sculptures fashioned by the artist from steel rods - guard the threshold, like the mythical hellhound Cerberus.Beyond lies the nether region of the studio itself, a straggling network of barrel-vaulted caverns, several filled with crated artworks.Some of these are ready to be shipped to London, where the Royal Academy of Arts is about to mount a survey of his career.Presiding over this shadowy domain is the artist himself, dressed incongruously in a short-sleeved blue shirt, shorts and grey espadrilles."It's very basic," Ai, 58, says softly, referring to the austere spaces of the bygone brewery's cooling cellars."Most important, the building works as a metaphor for being underground. And I am used to that, because I have been living underground since I was a baby."It is less than two weeks after his arrival in Germany following the sudden return of his passport, which the Chinese authorities had confiscated and withheld for more than four years.His bloody-minded skirmishes with the Communist Party of China have won him, outside his homeland, a degree of influence that he freely admits his art and architecture would not have secured by themselves."It takes a monster as big as the state to turn me, an ordinary artist, into an innocent hero."Indeed, art is now exclusively a form of political activism for this self-appointed scourge of the Chinese government, who draws attention to the ruling party's infringements of human rights by masterfully manipulating social media.Everything he does as an artist, then, must be seen through the prism of politics.Following a 12-year stint in the US , spent mostly in New York, Ai returned to China in 1993. He travelled home to be with his ailing father, the poet Ai Qing, who died in 1996.For Ai, a serial provocateur, defiance is second nature. A year or two after he was born in 1957, his father was exiled for expressing liberal views, to a village on the edge of the Gobi Desert, in the remote Xinjiang province of north-west China.Ai spent his youth there until the death of Chairman Mao in 1976, when the family was allowed to move back to Beijing and he enrolled at the city's film academy.There have been a series of detentions, monitoring, imprisonment, house arrest, and the removal of his passport.For now, he is relishing the freedom of life away from surveillance. Is he considering a return to China in order to keep sowing seeds of dissent?"If I can, I will return to China," he says. "I cannot predict the fall of a party, but China will become more democratic."How can he be so sure? "The whole world is changing. And China, with such a large society, can only meet the challenge of the future by having essential qualities such as freedom of speech, civil rights, human rights." ..