There are rules for zero/definite/indefinite article. And I don't get why we use 'the' with word 'mountains' in the next sentence:
I like to spend holidays in the mountains.
As for me the correct rule for this case is speaking about things in general, which states that we should use no article (zero article), like in 'I afraid of spiders.'
So why we use 'the' + 'mountains' ?
... [is idiomatic], not [necessarily] because 'zoo' has already been mentioned [previously] ... : it is equally acceptable to use the definite article in expressions like
"We're going to the seaside." /
"We went to the opera three times last year." /
"We often go to the cinema''.
– Edwin Ashworth Feb 13 '21 at 16:49