Where can I get the calendar embedding code?

Rather frustratingly the docs mention one:


and the web is plastered with references to one:

not to mention loads of articles looking at how to fix the refusal to load it due to cross site security settings.

But the doc does not tell me where to get one, and UI does not either. How can I get a calendar embedding code?

You can find it there:

Aaargh, thanks for that. nIt’s hidden until you share the thing! Down one level.! Doh!