«Is the military factory at the other side of the tunnel, or is that where the mining is done?»
This mining was done "here" — right where the hero stands: "..._here_ was where the raw materials had been mined for the military factory on the other end of the tunnel" — I have made two changes:
1) Past Perfect ("had been mined") — because the mine (as well as the factory, which is mentioned earlier in the game) had long since been abandoned by the time the hero visited it. I had overlooked it when translating and so did I during the many re-reads...
2) I changed "at the other side" to the less(?) ambigous "on the other end".
Should I add something like "...for the military factory _which was_ on the other end of the tunnel" to make it clearer?
«No, it's not clear to me.»
Hmmm. So, what about extracting this last clause into a seperate sentence so that the final version will be:
«I stood at the bottom of the ancient open mine. Possibly, here was where the raw materials had been mined for the military factory which was on the other end of the tunnel. The entrance to the tunnel was in the south.»
It has become more wordy and I am not sure I have corrected the drawbacks you indicated. But I have tried.
What do you think?