It’s a section ("/all-content/") with its own layout. This is a simplified version of the layout:
<!DOCTYPE html>
<html lang="en">
<head prefix="og: http://ogp.me/ns# fb: http://ogp.me/ns/fb# product: http://ogp.me/ns/product#">
<meta charset="utf-8">
<xbase href="file:///mnt/websites/xxxxxxxx/public">
<title>All the Posts!</title>
<style>
</style>
</head>
<body>
<h1>All the Posts!</h1>
<p>This is a copy of all posts on the website. To download the latest version, visit...</p>
<p>TOC:</p>
<ul>
{{ range .Site.RegularPages }}
<li><a href="#{{ substr .RelPermalink 1 -1 }}">{{ .Title }}</a></li>
{{ end }}
</ul>
{{ range .Site.RegularPages }}
<h2 id="{{ substr .RelPermalink 1 -1 }}">{{ .Title }}</h2>
<p style=""><a href="{{ .Permalink }}">{{ .Permalink }}</a> - {{ .Params.sdate }}</p>
{{ .Content }}
{{ end }}
</body>
</html>
I should warn you, however, that I’m not fully expert in Hugo; others in this forum may be able to give you much better solutions. This is just something I could come up, which works fine for me.