If the specified page does not exist, many websites will not just display a 404,
Navigate user actions by displaying search boxes and links to related information.

For example, Github displays not only a 404 but also a search box and related information links.

An example
https://github.com/redmine/redmice

However, in the case of Redmine, if the entered issue-no or project-identifier does not exist,
it simply displays 404, a search box, and a link to the TOP screen.

An example
https://redmine.org/issues/99999

h2. Proposal

If you make it possible to display messages and links created on each site instead of simply displaying the fixed phrase of 404,
I think that you can navigate the user's actions and use Redmine more effectively.

I want a search box, a link to the TOP screen and related information, and an image.

We can deal with it by changing render_404 of controllers / application_controller.rb,
But it is not a very good way.
Please let me know if there are existing methods.