We need to do that slightly differently, based on this example: https://gohugo.io/templates/taxonomy-templates/#site-getpage-for-taxonomies
{{ $taxo := "difficulty" }}
<ul>
{{ with ($.Site.GetPage (printf "/%s" $taxo)) }}
{{ range .Pages.ByWeight }}
<li><a href="{{ .Permalink }}">{{ .Title}}</a>
<ul>
{{ range .Pages }}
<!-- this also lists the content pages associated with the term;
remove if not needed. -->
<li>{{ .Title }}</li>
{{ end }}
</ul>
</li>
{{ end }}
{{ end }}
</ul>