Reporter, BBC Click
The idea of having a virtual you following the real you around may seem rather strange - for those of us used to having our feet firmly on the ground.
But the creation of a virtual Berlin lets people be in two places at the same time - as 20km of the city has been faithfully replicated into an online world.
By the end of 2008, 50,000 buildings in the German capital are expected to have been copied into the virtual world.
"While Second Life and others worlds offer some stylised versions of cities - Twinity uses the 3D mapping data currently used for things like satnav and Google Earth," said Jochen Hummel, the chief executive of Metaversum - owner of Twinity.
"One by one each building is then made to look as it would in the real world," he said.
Twinity's Berlin, which it calls a "metaverse" has been created by taking pictures of the city and using them to build 3D facades.
Volunteer developers may soon be encouraged to add their own or adapt existing ones, like users updating and adding entries in Wikipedia.
Emphasis on realism
While many online worlds are put to frivolous uses, Metaversum sees Twinity as a step beyond gaming.
"It's a space for virtual tourism," said Mr von Hardenberg. "The realism of this platform could help you plan a trip here, or just help you get your bearings before you arrive."
So far the closest many come to wandering around the globe is through 3D-mapping applications such as Google Earth that provide a snapshot of places.
Twinity emphasises realism, but the mantra for the virtual world is "be nice".
Mr Hardenberg hopes the platform will gain an audience beyond the core male gamers and attract more women.
"It's a social environment for meeting people, visiting galleries, or online shopping. Users are encouraged to create avatars that look just like them so they'll be recognised and to use their real names," he said.
Twinity has one advantage over reality when it comes to transport because there are no cars and visitors simply teleport to key locations.
Virtual Yellow Pages
Joining Berlin soon is London where another company is re-creating the city not just based on reality, but mapping it by inch-for-inch.
Near Global is launching in 2009 with the promise to offer the most accurate 3D version of a city ever produced as a virtual world.
While Twinity allows any company to buy its shops other than landmark stores, Near Global will offer a faithful copy of what users would find in reality.
GPS phones could be used to map actual movements to this virtual space, or phones could be used to go online into the virtual London to see what's ahead before getting there.
Londoners will also be able to know where to find anything they want by travelling there virtually - if it were to become popular, it might work as a Yellow Pages of its day.
"We don't search for stuff on a day-to-day level, we discover things," said Alex Wrottesley, the founder of Near Global. "Yes some people go out to buy a pair of socks but lots of people go out to look and see what's available.
"Information is not organised like that online and there's nowhere where that's all put together, and certainly not on an interface that's so intuitive to explore," he said.
At the moment only a few streets of the city are rendered.
But he firm hopes once the virtual London is complete real companies will get involved and offer services through "channels" on its website.
These could be free or require subscription, for instance, for entertainment companies offering live coverage of events or London's tourist board offering a Victorian experience of the capital.
All users will access virtual London and have the option to visit galleries or clubs like in real life, by paying to get access to the extra layers or "channels".
Companies might then be able to commercialise the opportunities offered by such a detailed virtual world.
Rather than using avatars, virtual London is turning to shards of coloured light.
"If you give people a physical presence in a world, you are asking them to make some very big statements on day one. I don't really want to do that. I don't really want to dress up to go to the shops.
"I want to feel I'm there, not that's I'm creating an alternative persona to inhabit there," said Mr Wrottesley.
Like Twinity where there are no cars and users can teleport to key locations.
Breaking away from reality further, there is no litter on the London streets, although there are litter bins, and again no weapons or traffic - beyond the occasional red bus.
Mr Wrottesley said it took around six months to properly re-create a city centre, and his company's next target was likely to be Moscow.