"In the middle of Germany"
This sentence explains what is "in the middle of Germany" these phrases act as the subject of the sentence.
"The tallest mountain in the range"
In this sentence the tallest mountain in the range is named.
"The trees", "many"
This sentence describes the trees. The second half of the sentence uses the subject "many" to refer back to the trees.
"the trees"
In this sentence the trees are doing the creaking and groaning.
"the mountain"
The mountain is the subject because it is what is being described as haunted.
"This witch"
The sentence explains what the witch does that makes people think that the mountain is haunted.
"her spirit"
This sentence describes her spirit as rising once a month.
"Locals and tourists"
The locals and tourists are the ones doing the verbs of gather and drink.
"the Brocken"
The Brocken is described in this sentence.