adjective describing middle distance (neither near nor far)
Solution 1:
While not directly related to distance and sometimes having a slightly negative quality, you could consider middling (which can be an adjective or adverb)
of middle, medium, or moderate size, degree, or quality
as in
They drove a middling distance, not quite halfway through their journey.
or
She traveled only middling far, taking in sights along the way.
Solution 2:
I would use "moderate distance" in this context.
Solution 3:
Any of "midway", "partway", or "halfway" could work, depending context. Of the three, "partway" is the most general.