What lies between shadow and light: Hints and solution

[TheDarkFanumbra]

I looked a bit at the puzzle and I found that as an idea, we can...

Spoiler below!

...put the image names together in some way. They are:
conc_thecastlehallwas
conc_therewassomething
conc_omniousthumping

And the new one from the puzzle solution page:

conc1x_somethingcalled

What this means, I don't know, but here are a few notes and possible answers (will be updated over time):

The 1x could mean it's the first words to be used in the solution. However, there is not even proof my theory is correct.

A few ideas what it may be:

Something called the castle hall was... (I couldn't make sense out of the rest)

Something was ominous thumping.

There, the castle hall ominous thumping was something called...

Any ideas? Do you think I'm on the right track?