Four days is a lot. Helsinki is not that large (or exiting). But it's not going to be a waste of your trip, depending what you're after. The nice touristy places are;
Suomenlinna, a 15 minute ferry ride from the market square (Kauppatori, which is nice in itself) is pleasant on a sunny day, and there's some nice sites and enough food places for an afternoon stroll/hike.
Design Museum and Architecture Museum are both nice,relatively small, so you can do both, and treat yourself in the Pavilion set-up in between the two museums (only this summer in light of Helsinki Design Capital)
South Helsinki shore (maybe rent a boat!) or just take tram 3b (or 3T since in the end they all come out in the same places) walk to Café Ursula through Kaivopuisto. The neighbourhoods Ullanlinna and Eira to me are the nicest in Helsinki and I've never seen so many Jugenstil buildings together. For a unique experience go to Shaslik Russian restaurant, or for fine dining to Chef & Somelier, for an informal bite (but confusing menu system) go to Carusel along the shore, but for a great view take a little ferry to The Boathouse.
You can also take the ferry to Pihlajasaari (from behind Carusel) to get a taste of what the archipelago experience would like: imagine yourself on an island like that with only some other summer cottages and friendly summer-mood people. Super tranquil. But maybe hire a kayak somehwere and do the real thing for a day.
Modern Art is good at Kiasma museum.
The most pleasant stroll is Esplanadi, and you're bound to go there if you're in the center, and it has all the Finnish design brand shops. There's also an outlet further away from downtown, with a direct tramlines 6 and 8.
Senatintori (Senate square) is impressive.
Tip: when I have time to spare in a city I get on just any random tram or bus to see what the locals live like, just outside the center. Tram 3B/3T go in an S so, you'll be back where you started. The Zoo bus from Central Station (#11) -even if you don't actually go to the zoo- also shows an interesting variety of neighbourhoods. You could also take the metro to its farthest point (and back).
If you have an extra day, outside of Helsinki you could consider Turku (2 hours by train) which is a much more preserved old city, or Porvoo which is even more quaint and smaller, and there's an old boat which goes there (consider taking a train or bus back, or vice versa). Also Fiskars is a nice trip if you happen to have a car anyway. http://www.fiskarsvillage.fi/en

Restaurants and Cafés that might not feature in the guidebooks (all on http://eat.fi/en/helsinki):
- Kitch - in the cobblestone street by the entrance of Hotel Torni. Nice lunch place with great food and exceptionally friendly staff
- Juuri - make reservation ahead in this small but pricy place for a Finnish take on tapas
- Spis - the latest Olo and other Michelin star restaurant wannabe
- Tori - for a slice of hip Punavuori (Design District and young-at-heart neighbourhood)
- Kämp Cafe and for more formal dining (great chef) Brasseri Kämp
- Fazer Café (pron.more like fawtzer) for your bulk shopping of Fazer chocolates to take home
- Kappeli for the full Esplanadi experience- coffee
- Café Jugend for brunch if you're around and it's raining - it's a beautiful indoor space, again, jugendstil

Shopping
- Stockmann for everything and anything
- Kämp Galleria for the high-end brands
- Punavuori/ Design District if you have time and like serendipity, starts at Uudemankatu
- Kauppatori market for souvenirs

See also:
http://guide.fi/
www.visithelsinki.fi/

Posted Jul 01, 2012

Hi! Restaurant GAIJIN is delightful and rates as some of the best sushi I have had in years.

GAIJIN
Bulevardi 6
00120 Helsinki
reservations: +358103229386
info@gaijin.fi
www.gaijin.fi

Also, the Belge Bar & Bistro was a relaxed place with a casual 'pub' atmosphere in the middle of the shopping area:

Belge
Kluuvikatu 5
Tel. 010 76 63590
www.belge.fi

I'd love to say 'be sure to take a bike ride' but I have no idea what December has in store... so good luck and fun travels-

Alisha

Posted Jul 01, 2012

Hi! Restaurant GAIJIN is delightful and rates as some of the best sushi I have had in years.

GAIJIN
Bulevardi 6
00120 Helsinki
reservations: +358103229386
info@gaijin.fi
www.gaijin.fi

Also, the Belge Bar & Bistro was a relaxed place with a casual 'pub' atmosphere in the middle of the shopping area:

Belge
Kluuvikatu 5
Tel. 010 76 63590
www.belge.fi

I'd love to say 'be sure to take a bike ride' but I have no idea what December has in store... so good luck and fun travels-

Alisha

Posted Jul 01, 2012

I know who I'm contacting should I ever find myself heading to Helsinki! These are answers are beyond "good."

Posted Jul 02, 2012

My wife and I spent 5 days in Helsinki after a week in Tallinn, Estonia (she is Estonian). As for not having anything to do, that's absurd. The center city, Old Market Hall and market place, Senate Square, and harbor area are fasinating and lovely. We were luck enough to be there when they had their annual Samba Carnaval and Parade, which was incredible. As mentioned, the trip to Suomenlinna, which is a World Heritage Site, was just fantastic. The ferry only takes 15 minutes and you get to see, and get a perspective of the magnificent harbor. Plan on 3-4 hours.
Also not to miss is the Uspenski Cathedral and the Temppeliaukio church (the rock church) which is like being inside a work of art, and not to be missed.
Outside of Helsinki (we rented a car) we loved Hvittrask, the home of architect Saarinen, and Ainola, the home of composer Jean Sibelius. Not to be missed is the short drive to Porvoo, an idyllic town of wooden houses. It's a great place for lunch and has lots of shops and craft workshops.
Helsinki has many fine museums, including the City Museum which tells the story of Helsinki's history.
Lastly, if this doesn't keep you busy, take the fast ferry to Tallinn (90 minutes) to see, next to Prague, the best preserved medieval city in Europe. The old town is an absolute delight.
As far as Helsinki restaurants, we loved Kuu, Fishmarket, and Sipuli for lunch.
Lastly, the Finns love the sun,and you'll find them outside, walking on the various islands. We loved taking the causeway out to Seurasaari Folison, a fasinating small island just NW of downtown.
You'll really enjoy Helsinki.

Posted Jul 04, 2012

There is an Italian restaurant adjacent to the Klaus Hotel that was really incredible. It blew my mind. Definitely add that to your list.

And yeah...the answers above are really frickin' thorough. Love to see that!!

Posted Jul 15, 2012