Content is one of the most valuable things online, yet we still allow it to remain hidden from visitor's eyes. One that is available, but can't be seen is very similar to non-existing one. The content is dependent on the link that leads to it, which means that once we hide the link, it can no longer be accessed through regular browsing, but only by knowing its exact URL. This can be a problem for both people and search engine robots.
As you can see, the label "menu" is barely visible and its visual weight is offset by the rest of the visual content on the page. As a result, first-time visitors might not even notice it, so they will overlook the fact that interaction with the red bar is possible. Statically perceived, this bar does not give initial indication to be functional, which makes it even easier for a person to skip through it. Interaction happens only when the vertical position of the cursor is within the boundaries between the top of the red bar and the red line below. Then we see the following result:
Now the menu is activated, but the result might not have been intentional at all. If we see again the white space above the red line in the previous screenshot, we could not assume that it will immediately behave differently on mouse over than the white background color. Since this space is larger than the red bar that acts in the same way, users might only accidentally enable the menu and see the additional content. This way, the "archive" category that probably makes for most of the content on the site, could potentially remain invisible to visitors.
It's also not clear if the content in this menu could be accessed by something else than a mouse. With a keyboard it seems to be impossible for me, since the outline on the currently focused object is missing. There is no way to know if a "menu" link exists that can be followed by pressing a key. And even when possible, would the tab focus "rotate" only within the activated menu until it is closed again with the same action, or would there be a mechanism for skipping to the rest of the content? This shows that an interactive menu could sometimes create more problems than it solves. A simple list of links, even if they take valuable screen space and are distracting in general, can improve the overall content visibility.
This isn't to criticize this particular website, which by the way has a great content, but rather to show how minimalistic interfaces could adversely impact content visibility.