How to programmatically derive Windows Downloads folder "%USERPROFILE%/Downloads"?

The problem of your first answer is it would give you WRONG result if the default Downloads Dir has been changed to [Download1]! The proper way to do it covering all possibilities is

using System;
using System.Runtime.InteropServices;

static class cGetEnvVars_WinExp    {
    [DllImport("Shell32.dll")] private static extern int SHGetKnownFolderPath(
        [MarshalAs(UnmanagedType.LPStruct)]Guid rfid, uint dwFlags, IntPtr hToken,
        out IntPtr ppszPath);

    [Flags] public enum KnownFolderFlags : uint { SimpleIDList = 0x00000100
        , NotParentRelative = 0x00000200, DefaultPath = 0x00000400, Init = 0x00000800
        , NoAlias = 0x00001000, DontUnexpand = 0x00002000, DontVerify = 0x00004000
        , Create = 0x00008000,NoAppcontainerRedirection = 0x00010000, AliasOnly = 0x80000000
    }
    public static string GetPath(string RegStrName, KnownFolderFlags flags, bool defaultUser) {
        IntPtr outPath;
        int result = 
            SHGetKnownFolderPath (
                new Guid(RegStrName), (uint)flags, new IntPtr(defaultUser ? -1 : 0), out outPath
            );
        if (result >= 0)            {
            return Marshal.PtrToStringUni(outPath);
        } else {
            throw new ExternalException("Unable to retrieve the known folder path. It may not "
                + "be available on this system.", result);
        }
    }

}   

To test it, if you specifically desire your personal download dir, you flag default to false -->

using System.IO;

class Program    {
    [STAThread]
    static void Main(string[] args)        {
        string path2Downloads = string.Empty;
        path2Downloads = 
            cGetEnvVars_WinExp.GetPath("{374DE290-123F-4565-9164-39C4925E467B}", cGetEnvVars_WinExp.KnownFolderFlags.DontVerify, false);
        string[] files = { "" };
        if (Directory.Exists(path2Downloads)) {
            files = Directory.GetFiles(path2Downloads);
        }
    }

Yes it is special, discovering the name of this folder didn't become possible until Vista. .NET still needs to support prior operating systems. You can pinvoke SHGetKnownFolderPath() to bypass this limitation, like this:

using System.Runtime.InteropServices;
...

public static string GetDownloadsPath() {
    if (Environment.OSVersion.Version.Major < 6) throw new NotSupportedException();
    IntPtr pathPtr = IntPtr.Zero;
    try {
        SHGetKnownFolderPath(ref FolderDownloads, 0, IntPtr.Zero, out pathPtr);
        return Marshal.PtrToStringUni(pathPtr);
    }
    finally {
        Marshal.FreeCoTaskMem(pathPtr);
    }
}

private static Guid FolderDownloads = new Guid("374DE290-123F-4565-9164-39C4925E467B");
[DllImport("shell32.dll", CharSet = CharSet.Auto)]
private static extern int SHGetKnownFolderPath(ref Guid id, int flags, IntPtr token, out IntPtr path);

Try this:

string path = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile)+ @"\Downloads";