There are a few options for long single day and multi day trail rides in Victoria with most of the handy options close to Melbourne being located to the west and north-west of Melbourne. The reason I like these as a long day trip or multi day option is that you can leave the car at home and use V Line services to get to the starting point and then return from a different finishing point or to provide a shuttle return to avoid having to shuttle a number of cars.

The Goldfields Track is a good example of this type of trail which allows a few days of solid riding from Buninyong in the south up to Bendigo in the north with V Line train services at Ballarat, Castlemaine, Kangaroo Flat and Bendigo or single day options such as Castlemaine to Bendigo.

Similarly there are options to ride from Bendigo line across to the Ballarat line or vice versa or to use the rail option to gain some elevation for a return run back to another station.

For those that are interested in even longer journeys, there is a good forum on Facebook called Bikepacking Australia. This forum has lots of tips on gear, long distance rides and other related items and are largely focussed on MTB and fat bikes.

The other option a number of rail trails which can provide some long distance rides up to 134kms. Most of these are based around easy to ride surfaces but there are a number that in a reasonably natural state as well.

V Line Timetables	Link top V Line timetables.
Goldfields Track	The Goldfields Track stretches from Buninyong (south of Ballarat) to Bendigo and presents a good multi day trip with town or tent accommodation in between. There are links to bike and walking maps on the site. Note that the routes are not the same with some of the walking sections being bypassed by bikes.
Lerderderg Track	Part of the GDT network of which the Goldfields Track is part of. This portion runs from Daylesford to Bacchus Marsh. Made up of a series of gravel roads, fire trails, single trail, etc which can be followed by mountain bike. Note that MTBs are not allowed in the conservation area of the Lerderderg State Park. Blackwood is the only real accommodation option (apart from hike tents) along the way. Plenty of camping spots available.
Woodend to Castlemaine	This was a three day trek which Sam Knight and his mate Chris did over three days from the Woodend Station to the Castlemaine Station in late 2015. There are some notes which I exchanged with Chris prior to his trip which detailed a number of options which others can refer to. There are some GPS files of their trip as well as some maps and photos which others can use to plan their trip.
Woodend to Bacchus Marsh	Woodend to Bacchus Marsh is another good option which I have previously done on the road bike on the bitumen but could readily be done on dirt as well. For the fit, this could be done as a long day trip or split into 2 days with an overnight stop at Blackwood. The section from Woodend to Blackwood is reasonably hilly but a route via the Woodend trails down to Amblers Lane and up the Byers Back Track is a great option. The next section from Blackwood to Bacchus Marsh starts with a short sharp climb of 100 metres elevation before hugging the ridges. After picking up Mt Blackwood Road, visit Mount Blackwood before enjoying the 600 metre plunge down to Bacchus Marsh via the Blackwood Ranges track through the Lerderderg Park. Great views and great fun.
Rail Trails	Link to Victorian rail trails website.
Bike Packing	Bike packing website which you can get good information on for Australia wide rides and gear to take.