How does Fe2+ become Fe in sacrificial protection? I've searched low and high on the internet, but nothing to help me.

I know that zinc is oxidised in preference to iron, and that it "donates" those two electrons to iron.
$$\ce{Zn -&gt; Zn^2+ + 2e-}$$

But how does iron make use of those two electrons to revert back to iron when it turns into iron oxide, like so:

$$\ce{Fe^2+ + 2e- -&gt; Fe}$$

Doesn't the $\ce{Fe^2+}$ in the $\ce{Fe2O3}$ need to be dissolved in water? How can it be affected by $\ce{2e-}$ travelling along? Maybe I am missing something.
I think the point that you're missing is that $\ce{Fe2O3}$ is never formed when there is $\ce{Zn}$ in the system. When the metal gets oxidized, the electrons come from the $\ce{Zn}$, not from the $\ce{Fe}$. This is true even if the physical location of the oxidation is on the iron, since the $\ce{Fe}$ and $\ce{Zn}$ are connected and conductive, so all of the electrons on both are shared.