I have a WordPress instance running on my domain's root.

One WordPress page is located at www.example.com/product/. I placed some static HTML files in a path below that so that visitors can go to www.example.com/product/documentation/ where an index.html and other HTML files live.

Now I can access the static HTML files just fine, but when going to the WordPress site (i.e. www.example.com/product/), I get a 403 Forbidden error.

How can I make the static HTML files available at that URL while retaining access to the WordPress page?

Here is my .htaccess file (I think it is the unmodified default)

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

Sorry if this question has been answered already, but I have only found questions about problems with displaying the static content rather than the WordPress content.