The Old Lands is a gathering name for the entire area of Atys that was occupied by the homin nations before 2481. In 2481, all the homin nations were decimated in the Great Swarming, and the surviving homins fled to a new faraway land to rebuild there.
This 'faraway land' is the area of Atys that the game of Ryzom takes place in today. All of the current known world is in these New Lands.
The Old Lands today are nothing but an unexplored wilderness full of ruins with unknown pockets of homin civilisation. With a few exceptions, no areas of the Old Lands are currently open ingame; they exist mostly in the Ryzom canon.
It is known from the Legend of Oflovak Rydon that the Old Lands are far to the east of the New Lands (the lands that homins live in now). So far in fact, that the first person to travel between them on foot needed 3 years to complete the journey. The route between the Old Lands and the New Lands, the Route of Exodus, is now called Oflovak's Road.
Only a few regions of the Old Lands are currently implemented ingame.
Almati Wood is an area of the Old Lands, to be precise an area of the old Matis Kingdom that was overrun by kitins. This is why there is no animal presence in Almati Wood except for the kitin, and why players can only get to Almati Wood through special teleporters. By extension, this means the Kitins' Lair beneath Almati Wood is also in the Old Lands.
These areas were opened in the same event as Almati Wood, and were supposed to be situated in the desert and lakelands of the Old Lands, respectively. But while Almati Wood remained open, these areas were closed again. They are currently still ingame, but not accessible to the players.
Many more regions of the Old Lands exist in lore only.
It's assumed that all cities and towns are long in ruins, but the regions one would assume are still there.
Most likely all the same creatures that live in the current known world also exist in the Old Lands. And all homins that live in the New Lands today are descendants of homins that once lived in the Old Lands.
The Marauders are homins that never moved to the New Lands and still live in the Old Lands today. Very little is known about their society and culture. Only in recent years did they decide to conquer the New Lands for themselves.
The Kitin originate from the Prime Roots beneath the Old Lands. When homins first arrived in the New Lands, there were no Kitin there, neither on the surface nor in the Prime Roots. Only later did the Kitin pursue homins to the New Lands and set up nests there.
The lakelands of the Old Lands are known to have been inhabited by some aquatic animals that don't exist in the New Lands, like the Baldusa, the Prakker and the Sagass.