Now this is 'time travel' only in a metaphorical sense: you're not actually going back in time — you're just imagining yourself at another time. Or perhaps you don't even imagine yourself as being there, you simply imagine what it must have been like, how it must have looked (and sounded, and smelled) at that time. This is different from time travel as it is presented in novels and films: there, a character is transferred from his own time into a different time and then is actually there. Put differently, a time traveler in a movie would perceive a different world, the world of the past, while a museum visitor imagines it. Both may have some visual impression (and again, also impressions on the other senses, too) of that world. But where the time traveler perceives an independent reality, not subject to his will, the museum visitor shapes such a world in his imagination, and is therefore free to include whatever he fancies (he might for instance imagine his romantic partner sitting at that banquet table in an exquisite old-fashioned dress). By virtue of this difference, the museum visit isn't time travel in a proper sense, only in a metaphorical sense, based on some similarities in the experiences one would have.
In order to make this distinction as clear as possible, I have so far not mentioned a complication, which we now have to look at. The complication is this: even though we imagine (not perceive) the world of the past into which the museum invites us, we couldn't just dream it up ourselves. After all, the very purpose of the exhibition is to make us familiar with details about the past which we didn't know about so far. We learn something from it, something we didn't know before, and what we learn is obviously not coming from our imagination, but comes from the outside, channeled through its presentation at the exhibition. Where does it come from?
The exhibition will be informed, often by historical or scientific fact which we know about. Thus, if the exhibition is about dinosaurs, much of the information will come from science (what did a dinosaur look like, what were its dimensions, its color and shape, its typical movements, how would a typical environment have looked, which plants were there, and so on). It's science which reconstructs these things and can tell us how we would have to imagine them in order to keep within established facts. If the exhibition is rather about historical or cultural matters (such as the history of an island or the life and work of a composer, say), then that information comes from history. (History has methods that are somewhat different from those of science.)
So, from a historical exhibition, we can learn something about the real world, even though we look at the world of an instance of unreality. I call this the informedness of unreality by bits and pieces from the real world. This does not run counter to the general character of the unreal as imagined, as being a product of the imagination; it just shows that the workings of the imagination always take up some materials from reality and include, shape and develop them in the process of generating an instance of unreality. You can learn from an exhibition about the past just as you can learn from a movie or a novel, or a dream: for instance, if you are a reader of crime fiction, you might learn a bit from it about police procedure, or forensic science. Of course, it's only in there because the author has researched it and built it into the world of her story, and it goes without saying that there is no guarantee that it's not fictional — the author might just have invented some bit of science which was necessary for the narrative, but which isn't actual science. Even dreams include memories, thoughts and emotions from waking life as building blocks, however much they may rearrange and distort them; from these you may pick up things about yourself and your recent experience you haven't noticed (yet) while awake.
(Such informedness is in some respects a counterpart to sedimentation; just like the latter, the former results from the interplay of reality and unreality, resulting in a mix of both along the path. Instances of the unreal sediment into reality when they influence our views and actions; bits and pieces of the real make up the materials from which the worlds of unreality are created.)
 It's also sometimes called fictional export. See for instance Christy Mag Uidhir and Allen Hazlett, "Unrealistic Fictions", in: American Philosophical Quarterly 48 (2011), 33–46. This seems to be a very helpful notion, but I have to read up more about it.