Things to keep in mind booking ARNK international tickets [closed]

What you're describing is more commonly known as an open-jaw ticket. These are quite common and can be easily issued by any halfway competent travel agent, although you may have some trouble booking these online since most booking engines don't support them very well: you may get quoted the price for two one-ways, which is usually far more expensive. Calling the airline and booking directly may be an option.

The main "catch" is that you'll need visas for both ends of the trip, but in your particular case this is unlikely to be a problem if you're Australian and don't need any visas in advance to visit the EU's Schengen area or the UK. And even for those destinations that do insist on tickets out, border guards will usually be satisfied with a flight out from a neighboring country, although prebooking your transportation across the border (train, bus or whatever) won't hurt.

The answer by jpatokal is perfect, I have a little addition.

Imagine if you have a ticket from Australia to London with one leg only (SYD-LON), then from London you will go to Rome by a car or a train. Finally, you have another separate ticket to take you back home. Now is that a problem? not at all.

Same exact procedures will apply for your ARNK ticket, think of it as two separate tickets they just happen to be with one reservation number, and possibly a cheaper option than having two separate tickets like the example above.

To sum that up, there is nothing special about having an ARNK ticket or two (or more) separate tickets, not from the visa or other official related aspects.