Which quotations in 'Macbeth' are a good example of 'the gothic'?

There are multiple examples of the Gothic in
Macbeth.  Any reference to superstition is a Gothic reference.  So,
you can quote the witches at any point in the text to reference Macbeth as containing
Gothic elements. Another example seen in Gothic literature is the setting of medieval
times (castles, dungeons, etc.).

Also, the use of darkness
and blood are also seen dominantly gothic literature.  There are, again, many quotes
that you can use to reference these as well.

That being
said, perhaps one quote that stands out as exhibiting typical Gothic features
(references to the supernatural and the typical Gothic setting of the castle) is one
from the Porter:

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Here's a knocking indeed! If a
man
were porter of hell-gate, he should have
old turning the key.

[Knocking within] 750
Knock,
knock,
knock! Who's there, i' the name of
Beelzebub? Here's a farmer, that hanged

himself on the expectation of plenty: come in
time; have napkins
enow about you; here 755
you'll sweat for't.
[Knocking
within]
Knock,
knock! Who's there, in the other devil's

name? Faith, here's an equivocator, that could 760
swear in both
the scales against either scale;
who committed treason enough for God's sake,

yet could not equivocate to heaven: O, come
in, equivocator.

[Knocking within]
765

Here the Porter
references the castle by acknowledging that he must come to answer the gate to callers. 
Also, the Porter references the Devil (a supernatural element).