The Old World is the continent all of your characters are from.
The Old World is a medium-sized continent bounded by the Shining Sea in the east and the Sunset Sea in the west. The main land mass is 984 miles from its northernmost point to its southernmost point, and 840 miles at its widest point.
The Old World supports a broad variety of ecosystems. In the north, the Mamrok and Kronam Mountain ranges support permafrost and tundra ecosystems that are inhospitable to all but the most hardy life forms. This frozen waste land gives way to a narrow, stony sub-tundra belt at the southern end of Mhunden Bay before yielding entirely to dry, temperate lands around the Ogele Steppes and the lands north of the Zuddak River .
In the east, the Zuddak Wilds are a colorful maze of canyon lands sporting dramatic views over sheer cliff walls that have been carved over the millenia by the slow flowing Zuddak River , which finds its source in the Gijazura Mountains on the shores of the Shining Sea . After exiting the Wilds, the Zuddak River meanders through the fertile Aesa Plain, which forms the breadbasket for the civilized populations of the Old World.
The Aesa Plain is bounded in the south by a ridge of tall mountains called Hith Amon, which divides the temperate middle region of the the Old World from the lush, heavily forested tropical region of the Celoneryn Jungle . The jungle is watered by an extensive river system which feeds the Celulinda, which flows westerward until it enters the Sunset Sea at Tinnu Bay.
The southernmost region of the Old World is dominated by the Zavgeh Desert, whose ring of low mountains prevent most moisture from reaching the interior of the continent at these latitudes. Low, rolling hills separate the coastal face of the Zavgeh Mountains from the sea.
There are two small archipelagos off the coast of the Old World. In the northwest is the Virnistal Islands, which are rugged, stony, and subjected to brutal ocean storms rolling westeward from the Sunset Sea . South of the Celoneryn Jungle is Zengin Island, which is famed for its strange and exotic wild life.
Monsters are rare on the Old World. The dragons all died out long ago, and have ascended into legend. Nowadays, Giant Spiders are the most terrifying monsters the average person sees in their lifetime. Although the continent sports a wide variety of sentient species (see Playable Races in the Player's Handbook), the animal life is limited to Beasts (as a category in the Monster Manual).