OSX: Where are my external drives?

From Stereomerger

From a developers point of view, Mac OSX have two file systems. One is the user friendly one you can see in the Finder and most other programs. The other one is the actual file system. Stereomerger can unfortunately only use the latter one as that is what Java offer.

What does this mean?

That mean you will see there are some different paths to many things compared to what the Finder shows.

External drives and network drives for instance, can be found at /Volumes/

For more info, read this: OS-X Paths