By chance I drove past a sign for a wetlands walk near Hastings on the Mornington Peninsular so I walked it and it was quite pleasant. It is a short 3.5 km (each way) walk but worth doing if you are down that way or even want to do a one hour drive there. Note that it is not isolated and you can see buildings from many parts of the track so don't do it if that bothers you. This wetland area has the most southerly mangrove swamp in the world. The following link has the details to this and other walks in the area.
http://www.themorningtonpeninsula.com/W ... nds%20Walk