You can typically find and download this track through the following community hubs:

: If you receive an error stating the file is "damaged" when trying to open it with WinRAR or 7-Zip, this is normal. .pkz files are encrypted game archives and are intended to be placed directly into the mods folder without being extracted. Issue Installing Tracks - MX Bikes Official Forum

The file is a track mod for the simulator MX Bikes , which features a replica of the real-world Underground MX facility in Kemp, Texas. Where to Download

: The track should now appear in your in-game track selection list.

: The primary site for game modifications. You can search for "Underground MX" directly on MXB-Mods.com .

Once you have downloaded the .pkz file, follow these steps to use it in-game:

: Navigate to your local documents folder for the game: Documents\PiBoSo\MX Bikes\mods\tracks