I would greatly appreciate to get clear descriptions on the following questions.
1. Is there a gym in the hotel OR is there any gym in the hotel? Why?
2. It is said "in" is usually used with the street when an activity is being done like playing, striking, biking, etc. How about driving? Can we say "he is driving in the street"?
3. Some verbs like stop get doubled in the last letter because of the letter "o". How about some other verbs which follow this rule, but aren't get doubled in the last word like prefer?
4. Which one is correct "sea" or "the sea"? Can both be used? If so, in what situations

Question

I would greatly appreciate to get clear descriptions on the following questions.
1. Is there a gym in the hotel OR is there any gym in the hotel? Why? 
2. It is said "in" is usually used with the street when an activity is being done like playing, striking, biking, etc. How about driving? Can we say "he is driving in the street"? 
3. Some verbs like stop get doubled in the last letter because of the letter "o". How about some other verbs which follow this rule, but aren't get doubled in the last word like prefer? 
4. Which one is correct "sea" or "the sea"? Can both be used? If so, in what situations

Answer

1) yes both are almost fine but "any" doesn't add anything to "a" unless there might be are multiple gyms, so "any gyms" would be better
2) yes
3) yes.  English is an organic language some do and some don't
4) I am going off to sea.  I went to the sea.  They mean different things but both work.  (the first suggests becoming a sailor, the second is a visit)