The main thing we learn about Zanak (from Doctor Who's The Pirate Planet) is that it goes where you want it to, thanks to giant teleportation engines and a hollowed-out core. But actually, when the Doctor takes to the skies and zooms over the planet's surface, we see a fair amount of different scenery, including forests, mountains and a desert. (Plus, of course, materializing around other planets would logically mean that Zanak's climate changes somewhat every time it changes location. What are the odds that it would always appear around planets that are exactly the same distance from their respective suns? So that's a kind of variation as well.) Note also the weirdly lumpy Adobe-rock style of Zanakian architecture, which proves limitless wealth can't buy taste.