I feel the environment is an important aspect of a physical journey, while others don't. Keep in mind that English is all about expressing your view, and as long as its proven then thats fine.
The physical journey cannot be a physical journey without some kind of inner journey as well, but lets not get into that seeing as we're only describing physical journeys for our HSC. The environment plays a big impact in the difficulties of a physical journey, the milestone if you wish.
Lets use Harry Potter 1 for example, only because I doubt many people wouldn't have seen it.
When Harry travels towards the Philosophers Stone the environment plays an impact on his feelings and in tern his actions through each obstacle he must overcome. Each obstacle becomes more challenging, but the environment he's placed in, makes him push forward.
A journey must be hard in a way, much like the climbers of Mount Everest. Half the journey itself is the conditions and environment, and it is that which brings out the sense of accomplishment and the change in yourself, change of your thoughts and just an impact overall. There will be people who disaprove of my point, but you just need to explain your ideas.