Sorry it took a while to get back to you guys - I was busy trying to finish some other stuff!
Sorry I don't have any links at the moment, but I want to second what was said about port cities vs inland areas. Port cities were often extremely diverse, as were the crews of sailing ships in that era. If that's the setting you're working with, dig around in those sources.
What kind of travel? Immigration? Scientific research? Trade? Working people like the Chinese who helped build the US railroads? Elites on pleasure cruises? Colonial peoples forced into the imperial army or navy? Indigenous peoples taken from their homes and put in human zoos"? If you find general sources that address all this, I'd be interested too, but I imagine this'll be hard to find without being more specific.
I think in terms of travel I am thinking of two characters. One would be a male who would have come to England, probably London or maybe Liverpool, at a young-ish age like maybe 11 or so from some place. I haven't decided whether South or Central America (leaning more towards South America). The problem is I don't know how he would have gotten from South America to England in the late 19th century - I mean, yes by boat, but I mean, under what circumstances?
From the options you mentioned I'm intrigued most by colonial people who were forced into imperial armies. I'm also interested in potential trafficking of South American natives across the Atlantic to England or just Europe generally. Do you know where I might find more resources if you have them?
As for people in zoos, I know a lot about Africans in that situation but did not know that there were other natives that suffered that humiliation. Do you know more about it?
http://www.h-net.org/reviews/showrev.php?id=8797
Gretchen Holbrook Gerzina, ed. Black Victorians/Black Victoriana. New Brunswick and London: Rutgers University Press, 2003. x + 222 pp. $24.95 (paper), ISBN 978-0-8135-3215-8; $62.00 (cloth), ISBN 978-0-8135-3214-1.
I just got this book! Thanks so much for reccing!
What part of Western Europe? Port cities like Liverpool and Marseilles would have a diverse population, while inland rural areas were usually entirely white.
Here's a page about the black population in London:
https://www.oldbaileyonline.org/static/Black.jsp
See also
Black Victorians/Black Victoriana by Gretchen Holbrook Gerzina.
It would probably be Liverpool and London that I'm working with. I'm curious about Italy though, like Venice. I know I am planning on researching stuff to do with the individuals from the Ottoman Empire and Italy.