We're starting a new Marathon adventure-- this time fighting the Pfhor in Italy of the past in third party scenario Tempus Irae!
In this episode there's a castle filled with classical art, walls that explode, and aliens. It's always aliens.
Tempus Irae can be played, like the other Marathon games, using the open source Aleph One engine which you can get here for Windows, Mac and Linux:
http://source.bungie.org
Tempus Irae and other third party scenarios for the Aleph One engine can be downloaded here: