In Limbo (Canto IV)

And after that I fell
as a man-whom sleep hath seized,
breaks my lethargy
an heavy thunder

Dante's fainted, and is being relieved by a thunder's blast on the shores of Acheronte river
upon the other verge I find me
of the abyss's valley dolorous
That gathers sound of eternal laments

Obscure, profound it was, and nebulous
so dark my eyes can’t catch any living motion
Here I found myself in the blind world
where sparkles of life can burn but of damnation

Dante's describing the place where he founds himself as obscure, profound and nebulous; he also says to be unable to see anything
Let us go, for the long way...
And there now, we are listening
No lamentations, but only sighs
That tremble made the everlasting air

Dante and Virgilio are about to descend when Dante focuses on his hearing only sighs
"here we are
entering the hell with fear
this the first circle, will be the home of my pain,
my punishment is to stay here,
where no one is sinner
only not baptized....."

Virgilio tells him that Limbo contains souls of people who were not baptized, and he is part of it too
Obscure, profound it was, and nebulous
so dark my eyes can’t catch any living motion
Here I found myself in the blind world
where sparkles of life can burn but of damnation

Dante's describing the place where he founds himself as obscure, profound and nebulous; he also says to be unable to see anything