Gentlemen,
If you are in free-roam, you can call up the globe and select another environment. All environments are available.
Click the Globe button—fourth from the right in the bottom right corner—to bring up the globe.
Drag the globe with the right mouse button to reach the environment.
Seas are red, harbors are yellow, and the current environment is green.
Zoom in with the mouse wheel. Put the mouse pointer over a dot to make it grow larger and click the left button to turn it green. Click the Go button.
If you are in a mission, the button for the globe is usually inactive. You get the globe when you reach the limit of the environment. Your selection is limited to those environments that the creator has included in the mission.
Tom, there are no other environments beyond those listed in free-roam.
Regards,
Marty