Black and White Lodge seem to be both: real places and dreamlike realms that characters have experienced in a common dream. In the last episode of season 2 <PERSON> enters the Red Room through the curtains at Glastonbury Grove and Sheriff <PERSON> sees him disappear. There is no indication in that episode that <PERSON> and/or <PERSON> are dreaming. The same goes for <PERSON> and <PERSON>, who entered the Red Room prior to <PERSON>.
<PERSON> explains that "the White Lodge is a place where the spirits that rule man and nature here reside. [...] There is also a legend of a place called the Black Lodge, the shadow self of the White Lodge. Legend says that every spirit must pass through there on a way to perfection. There, you will meet your own shadow self." To my knowledge, it has never been said that Mr. <PERSON> is <PERSON>'s shadow self, but it is likely that <PERSON> and shadow self are the same. 295
Mr. <PERSON> managed to leave the Red Room and started a criminal career in reality.
In episode 3 of season 1 <PERSON> dreams of the Red Room, where he meets <PERSON>, who tells him the name of her killer. (He forgets the name). In episode 9 of season 2 <PERSON> reads from a page of <PERSON>'s secret diary, where <PERSON> refers to the same dream. In Fire Walk With Me <PERSON> appears to <PERSON> in a dream, where she tells <PERSON> to write in her diary that the good <PERSON> is trapped in the Lodge and can't leave. When it comes to dreams and Lodges, time isn't linear.
But, one might argue that the whole of Twin Peaks is a dream anyway. <PERSON> reports to <PERSON>, <PERSON> and <PERSON> that "we live inside a dream." <PERSON> tells his <PERSON> dream, where <PERSON> says "We're like the dreamer, who dreams and then lives inside the dream." Then she asks "But who is the dreamer?" while she's looking at the viewer. With that in mind, I suggest that Black and White Lodge are dreamlike realms in a dreamlike realm, where daily reality is on a different level, less deep than the dream in the Lodges. Therefore reality as we experience it is more flexible in the fictional reality of Twin Peaks, and therefore it is possible for <PERSON> to travel back in time and save <PERSON>. 663