Hi,
I have a layover of 18hrs in Helsinki starting from 3:30 PM till 8 the next morning. Firstly, I would like to know whether I can come out of the airport ( I have schengen visa) ?
Secondly, how can I go about visiting Helsinki for a day? What all things can be covered.
I'll be traveling with a friend and interested in nature, culture and yes beers .

What month and day will you bee in Helsinki.?
It could be getting dark earlier depending on when you are there.

Do you have anything special you want to see
in Helsinki.?

12th september to be exact.

You can take the bus into Helsinki from the airport - as I recall, it was about an hour's ride and reasonably priced. Your best bet might be to just walk around as most things will most lkely be closed by the time you get into downtown and won't be open when you leave the following morning. Not ideal, but at least you'll see something.