She said that because he was able to answer any question related to nature and its beauty. He knows everything about it, even the tiniest details no other man could know. He actually inspired Danilka to love and awe nature, because of his great love for it.
I personally would say ancient castle in ruins...
My reason for this would be that the office building and the apartment in the city will be modern and won't have a Gothic feel to it...
The mansion in the countryside will be surrounded by green fields and well that scenario doesn't sound very dark and Gothic to me...
And well that castle in ruins will have a spooky side to it as it will be abandoned and especially at night will be a host to a whole range of spooky thoughts and ideas.
Frankenstein and the Creature share a love of nature because they once had a loving relationship. They had very high feelings towards each other, they had changed an abundance of times such as pity to disgust.
Hope this helped! :D
