Learn Polish: Gdziekolwiek by spojrzała ta kamera, widać tylko pusty mrok. - Wherever this camera might have looked, only empty darkness can be seen.

In Polish, universal concessive clauses with -kolwiek and the particle by always require the verb to be in the past-tense l-participle form, like spojrzała. The time period doesn't matter; the combination of by plus the past tense is what creates the hypothetical meaning of 'might look' or 'might have looked'.

Could we attach by directly to the verb and say Gdziekolwiek spojrzałaby ta kamera?

Yes, Gdziekolwiek spojrzałaby is grammatically correct and means the exact same thing. However, in these -kolwiek clauses, it is very common and natural to leave the floating particle by as a separate word right after the question word, as we see here with Gdziekolwiek by spojrzała.

What case is pusty mrok in, and why?

It is in the accusative case. The word widać (meaning 'one can see' or 'is visible') is an impersonal predicate that always requires the object being seen to be in the accusative. Because mrok (darkness) is a masculine inanimate noun, its accusative form looks exactly the same as its nominative form.

Could I use ciemność instead of mrok here?

Yes, but there is a slight difference in nuance. Ciemność is the standard, general word for 'darkness' or the complete absence of light. Mrok is more atmospheric and often translates to 'gloom', 'shadows', or 'murk', giving this sentence a slightly more cinematic or eerie feeling.