Making them 'real' is the problem we often run up against. I've heard a visitor describe our Disease Street as "smelling like smoky bacon crisps". Visitors' smell associations are often more disparate and unpredictable than those cued by other senses.
My new article on Jorvik Viking Centre and its use of smells over the last 40 years has just come out today in The Public Historian! online.ucpress.edu/tph/article-... if you can't access it and want to read it, let me know.