The core of Marz is a hollow sphere half filled by the Great Open Seaz – an enormous ocean teaming with all sorts of wildlife – much from Urth and long extinct there, but due to Marzian technology now thriving in the centre of the Red Planet. The Great Open Seaz has shores and beaches so is open to the populace for specialist holidays (even Sub-Layer Three can’t satisfy everyone all of the time). Indeed, Marzians will usually visit at least once a year to see the wildlife and take in the rays from the biggest artificial sun on Marz.