I use the Weaver II theme, and so I delved into creating a child theme for it, that would give me a 404 error page, and an HTML sitemap page. In reading the article about useful archive pages I came to see that an archive page is useful to the visitors to my site.
Custom 404 Page
I have created a custom 404 page that attempts to find the content the visitor came for, then it gives the visitor a way to search my site quickly, or scroll through a sitemap for my site, and lastly they can go to the homepage quickly. The goal of this page is to keep my visitors on the page longer. I am also trying out a plugin to capture 404 errors, so that I can decide how to permanently handle them.
I followed Yoast’s example and created a template that will list content from several ways to find what a visitor is looking for. One thing that Yoast suggests is that you do away with dated archives, so this page does not include the dated archives.
I found the article about how to make a useful archive page, and then created one. It includes dated archives as well as the sitemap categories, and a tag cloud.
Sitemap vs Archive
In the end I realized that I did not need both a sitemap and an archive page. I decided on the Archive, as my HTML sitemap. My reasoning for that is that this page is designed to help visitors, including bots, and the more ways to the content the better, as long as only one URL is being indexed. So be sure to make your archive/sitemap page follow, noindex.
You can use the articles to generate your own child theme or feel free to download a copy of my child theme, with sitemap and archive page templates, as well as a custom 404 error page.