List subfolders in sidebar navigation

It's... a little confusing but from what I understand you need subfolders...

Remember that VuePress sidebar is used to organize how the user sees the items in a specific order. The sources not matters name or where the .md file is. You can add from any path but is better to follow the Directory structure convention.

---

There are some considerations in your case.

Firstly...

For subfolders routes, you need to create a README.md (take it like an index.html). So, you need a Default Page Routing. Router expects that the ending /{page}/ has a /{page}/README.md

Try renaming your index pages to its subfolder like '{name}/README.md'.

For example media.md --> media/README.md.

Secondly...

There are some tree errors in your config.

I noticed you use sidebar: {} (as an object). This is intended to make multiple sidebars (different pages/sections), like in VuePress documentation Guide | Config Reference | Plugin |etc you see in its navbar. If this is your goal, you have to place all child items inside '/docs/' for example and create a fallback:

sidebar: {
    '/docs/': [
        '', // this is your docs/README.md
        // all sub-items here (I explain later)
    ],
    '/': [ // Your fallback (this is your landing page)
        '' // this is your README.md (main)
    ]       
}

Thirdly...

As I introduced before, you need to place all the items under that main.

Instead of creating a different route for each page, you can (after renaming I mentioned before) you need to remember that Sidebar (at least in the default theme) only have 1 route level. Their hierarchy levels are made by H2, h3, h4..., not by file structure.

BUT... You can organize your sidebar sections by grouping it. For example:

sidebar: {
  '/docs/': [
    '', // this is your docs/README.md

    {
      title: 'Getting Started',
      collapsable: false,
      children: [
        'gettingStarted/', // 'docs/gettingStarted/README.md' if you renamed before
        'gettingStarted/creatingFirstApplication',
        'gettingStarted/creatingFirstApplication/setup', // maybe better to move content to `creatingFirstApplication.md`
        'gettingStarted/installing/installation',

        // Maybe group all this in another another group if is much extense (instead of Getting Started)
        // or join into one file and use headers (to organize secions)
        'gettingStarted/understanding/why', 
        'gettingStarted/understanding/useCases',
        'gettingStarted/understanding/coreConcepts',
        'gettingStarted/understanding/architecture',
        'gettingStarted/understanding/gettingHelp',
      ]
    },
    {
      title: 'Guides',
      collapsable: false,
      children: [
        'guides/', // 'docs/guides/README.md' if you renamed before
        'guides/firstApplication',              
      ]
    },
    {
      title: 'Media',
      collapsable: false,
      children: [
        'media/', // 'docs/media/README.md' if you renamed before
        'media/downloads/brochure',
        'media/onlineResources/articles',
        'media/onlineResources/videos', 
      ]
    }
  ],

  '/': [ // Your fallback (this is your landing page)
    '' // this is your README.md (main)
  ]       
}

If you need split more, think in another section (instead of '/docs/' use each part as a new navbar item (like Guide | Config Reference | Plugin |etc)).

If not, you can also set the option sidebarDepth to 2:

themeConfig: {
  sidebar: {
    // . . . 
  },
  sidebarDepth: 2
}

---

I hope this helps you. :)

Note: Maybe I missed some route, so check it your self.

Note 2: Not run in local, but should be fine the structure/syntax. Again, check it and comment,

The answer above really helped us. We're running Vuepress 1.3.1 and ran into some issues using the sidebar groups example code above. (under thirdly)

We ended up with a fairly complex sidebar and had to structure it accordingly. Below is an abbreviated version of our config file. (whole config file)

module.exports = {
   // Removed other config options for readability 
   themeConfig: {
      // Removed other themeConfig options for readability 
      sidebar: [
         "/",      
         {
            title: 'AccuTerm',
            path: '/accuterm/',
            collapsable: true,
            children: [
               {
                  title: 'Mobile',
                  path: '/accuterm/mobile/',
                  collapsable: true,
                  children: [
                     ['/accuterm/mobile/quick-start/', 'Quick Start'],
                     ['/accuterm/mobile/colors-and-themes-settings/', 'Colors & Themes Settings'],       
                     ['/accuterm/mobile/connection-settings/', 'Connection Settings'],
                     ['/accuterm/mobile/keyboard-and-clipboard-settings/', 'Keyboard & Clipboard Settings'],
                     ['/accuterm/mobile/screen-settings/', 'Screen Settings'],
                     ['/accuterm/mobile/terminal-settings/', 'Terminal Settings'],
                     ['/accuterm/mobile/user-guide/', 'User Guide']
                  ]
               },
               {
                  title: 'Web',
                  path: '/accuterm/web/',
                  collapsable: true,
                  children: [
                     ['/accuterm/web/web-introduction/', 'Web Introduction'],
                     ['/accuterm/web/getting-started/', 'Getting Started'],
                     ['/accuterm/web/release-notes/', 'Release Notes'],
                     ['/accuterm/web/activating-accuterm-desktop-licensing/', 'Activating AccuTerm Desktop Licensing'],
                     ['/accuterm/web/batch-user-actions/', 'Batch User Actions'],
                     ['/accuterm/web/change-password/', 'Change AccuTerm.IO Password'],
                     ['/accuterm/web/clipboard-settings/', 'Clipboard Settings'],
                     ['/accuterm/web/connection-settings/', 'Connection Settings'],
                     ['/accuterm/web/creating-profiles/', 'Creating Profiles'],
                     ['/accuterm/web/creating-roles/', 'Creating Roles'],
                     ['/accuterm/web/creating-users/', 'Creating Users'],
                     ['/accuterm/web/font-and-character-settings/', 'Font & Character Settings'],
                     ['/accuterm/web/installing-accuterm-io-server/', 'Installing AccuTerm IO Server'],
                     ['/accuterm/web/keyboard-options/', 'Keyboard Options'],
                     ['/accuterm/web/mouse-settings/', 'Mouse Settings'],
                     ['/accuterm/web/sound-settings/', 'Sound Settings'],
                     ['/accuterm/web/terminal-screen-options/', 'Terminal Screen Options'],
                     ['/accuterm/web/terminal-settings/', 'Terminal Settings'],
                     ['/accuterm/web/web-profiles/', 'Web Profiles'],
                     ['/accuterm/web/rezume-session-resilience/', 'AccuTerm ReZume Session Resilience'],
                     ['/accuterm/web/phi-reports/', 'PHI Reports']             
                  ]
               }
            ]
         },
         ["/docs/jbase/", "jBASE"]
      ]
   }
};

Directory Structure

Hopefully seeing this example will help clarify sidebar groups. To see the whole sidebar and directory structure view it on github:
Vuepress config file
Vuepress directory structure