From Nightingale Wiki

The game puts a heavy emphasis on exploration, as the world of Nightingale is separated into many different realms that are connected by portals.

Concept Art from the official Website[1]

Biomes revealed through gameplay footage, revealed or teased through official material and concept art include:

Realms become more and more difficult as you progress.

Realms are about two-kilometer by two-kilometer blocks.[2]