Armadillo uses and relies upon what's called "best web practices". One aspect of this is what's referred to as cruftless links. A regular link to a specific web page would look something like this:
However, a cruftless link is much simpler, and doesn't need you to enter the filename, so it looks like this:
The reason this works is because the page is put into a folder with a unique name (in the above example, "page-name"), and the actual page filename is called "index.php" or "index.html" (or "index" plus any file extension). Web browsers will automatically load an "index" file if there is one in a folder, so there's no need to include it in the actual link -- hence the name, cruftless links.
Armadillo was designed to work with cruftless links, and RapidWeaver uses this type of structure by default. If you have renamed your page filename to something other than "index.php", then the "Visit Site" link will not display your Armadillo page correctly. As such, and because it is best practice, we highly recommend using cruftless links with your Armadillo site.
For more informations see the video explanation of cruftless links on the NimbleHost Blog.