[PART. SOLVED] Prevent Grav from "processing" a certain subfolder of my website

Hi,
I'm trying to somehow prevent Grav from rendering/processing a subfolder of some of my pages altogether.

Folders named "app" should be hidden but routable with the additional requirement that Grav leaves the content alone and let's my webserver process the contents normally. So enterin http://site.com/Page1/app into the browser will open the HTML or PHP app (index.php or index.html) without using Grav to render the contents.

Home
|--Page1
| '--app
|--Page2
| |--app
| '--Entry
'--Page3

If that is not possible, are there any oder ideas how to achieve this or something similar?

Kind regards!

Ok, so I'm just adding a /apps folder to the root of my grav installation and install my apps there in their own subfolder. Then I'm referencing them in my blog posts using the full path like test.domain.com/apps/app1