To obtain a visa for the country you wish to stay in most Schengen countries require:-
a return ticket
travel insurance for the duration
accomodation receipts - or a letter stating that you will be staying with....
A police check
bank statements showing that you are able to support yourself - in other words show that you have sufficient funds.
That is a general summary - there may be other reuirements for specific cuntries (eg I think you may have to present at the German Embassy and be finger printed)
Australia has bi-ateral trade agreements allowing one to stay in a number of countries for an extra period - eg you can stay in Germany and Italy for an extra 90 days if you meet the requirements (leave the Schengen and re-enter)
Your other option is that if you are walking you could leave the Schengen and go to the UK and walk - there are many paths there to follow - eg St Oswald's way, St Cuthbert's way, West Highland Way, Hadrian's Wall Path and so on. These could easily occupy you for the required exit of 90 days, and you could stay up to 6 months before re-entering the Schengen.