http://www.eurogamer.net/articles/2013- ... d-for-2014
The biggest change in design for The Witcher 3 is its shift to being open world like an Elder Scrolls game. Where you go and when you go is up to you. There won't be chapters or acts, and hero Geralt will apparently answer only to himself.
CDPR said The Witcher 3's world is 20 per cent bigger than Skyrim's, according to the GameInformer reveal (digested on NeoGAF), and will take 30-40 minutes to traverse. CDPR boasts that the new RedEngine 3 will stream all areas and eliminate load times. Whether this is true of entering interior areas, I don't know.
Coming to PC and the next console generation.