Sinatra Sub-Directory Views

I'm not sure exactly what you're asking, but you can render a view in views/admin by doing this:

erb :"admin/report"

If you're asking how to automatically look in subdirectories of views when you call erb :report, I'm not sure how to do that, and I don't think you'd want to (what happens if two views in different dirs have the same name?).

This is supposed to be an oversized comment. The answer provided by Alex is the correct one, but to be sure, this is a quote from official documentation:

One important thing to remember is that you always have to reference templates with symbols, even if they’re in a subdirectory (in this case, use: :'subdir/template' or 'subdir/template'.to_sym). You must use a symbol because otherwise rendering methods will render any strings passed to them directly.