Australia is such a vast country you may find you need more than three months to explore! If you wish to stay in Australia for more than three months you will need an Australia Long Stay Tourist Visa (Subclass 676 visa)
Please note you cannot work in Australia on a Long Stay Tourist visa. If you wish to work during your time in Australia you must apply for a working holiday visa.
Visas4Oz.co.uk offers two types of Australia Long Stay Tourist Visa:
6 Month Australia Long Stay Tourist Visa
12 Month Australia Long Stay Tourist Visa