SF_10.1, SF_10.2, SF_11.0, SF_11.1, SF_11.2, SF_12.0, SF_12.1, SF_12.2, SF_13.0, SF_13.1, SF_13.2, SF_13.3, SF_14.0, SF_14.1, SF_14.2, SF_14.3 - https://docs.sitefinity.com/for-developers-get-folders

GetAllFoldersInAlbum.cs

using System;
using System.Linq;
using Telerik.Sitefinity.Modules.Libraries;

namespace Telerik.Sitefinity.Documentation.CodeSnippets.DevGuide.SitefinityEssentials.Modules.MediaModules.Folders.ManagingFolders
{
    public partial class FoldersSnippets
    {
        public static IQueryable<IFolder> GetAllFoldersInLibrary(Guid albumId)
        {
            //gets an isntance of the LibrariesManager
            var manager = LibrariesManager.GetManager();

            //gets the images album
            var library = manager.GetAlbum(albumId);

            //creates folder under the album
            var folder = manager.CreateFolder(library);
            folder.Title = "FolderTitle";
            folder.Description = "Lorem ipsum dolor sit amet, consectetur adipiscing elit.";
            folder.UrlName = "FolderName";

            //always call the SaveChanges() method of the manager in order to commit the operation
            manager.SaveChanges();

            //gets all folders under the album
            var searchResult = manager.GetAllFolders(library);
            return searchResult;
        }
    }
}