By Land and Sea

Are you talking about a cruise TO Australia, from say, the US or are you talking about a cruise around that country? Big difference. And, are you saying that you want to cruise the country, get off and do a longer land tour and then somehow get back on at a later date? I've never heard of that kind of trip. What you may have to do is book two separate cruises, pay in full for both and then do your land tour in between. Cruise ships aren't basic transportation where you can come and go as you please and they won't let you book a portion of a cruise so you can do a land tour and then get back on the same ship on the next go round.

I agree -- there are no ships that I am aware of that allow you to leave and then return at a later date. If, however, the ship is in port for 2 days, you can book an overnight land excursion -- as long as you are back to the ship in time to sail.