Excuse me...come again?

What do you do when you are torn between the safe and easy route and the unknown and adventurous route?
Usually I would definitively express preference for the unknown, but now that I'm faced with that choice in a larger, life-route decision, I'm not so sure.
A Masters and then a PhD--thats easy and safe. I know how to go about doing that. I know the universities to apply to, I know how to write, and how to research. It is a safe path that I'm sure I would find happiness walking.
However, something alluring and unshakeable is lurking in the back of my mind. Service, health, refugees, poverty, culture: these things roll around in my mind and awakens the part of me that has always known that my place is not here, but elsewhere; somewhere abroad. My work is not the self-enriching work of the scholar but the work of a self-sacrificing servant to people unknown.
Do I have the courage to follow a dream when I do not even know where to start or how to prepare? I guess we'll see...