Stockholm to Turku — by sea or by air?
 

Are the ferries from Stockholm to Finland enjoyable, or just an orgy of overeating, overdrinking, and overshopping? It's 11 hours, either overnight or most of the day, versus a one-hour flight. The flight is more expensive, when you factor in the hotel savings for the overnight.

Family of 4, the two children are adults but we could do a 4-berth cabin for one night.

Once we get to Turku we're cycling on the archipelago, so we'll see some nature either way.

I would advice taking the overnight ferry. It goes really close to some beautiful small islands. Silja and Viking are really similar so I would choose the one that´s more convenient to you. Silja´s port is a bit further from central Stockholm than Viking´s, but it is close to a tunnelbana stop.

I recommend eating at the buffet restaurant. It is really nice and the seafood dishes are delicious. If you book by phone you can request a table by the windows. If you book online or onboard go to the desk early (before seating opens) and you may still get lucky with a good view.

As for the (over)drinking, if you travel on weekend then party people onboard are to be expected. The prices for alcoholic drinks are expensive in the ferry´s restaurants/bars, so it is usual to buy something from the taxfree shop and then have a party in the cabin before going to nightclub. It is a good idea to book a cabin in either A or B class as the cheapest classes are more likely to be noisy.

During weekdays the passangers are mostly pensioners and families with children so much quieter atmosphere. :)

What time of the year are you travelling? If it is summer then you will be able to see the small islands in the Swedish archipelago on the overnight ferry, otherwise you will need to take the day sailing, in which case there is no saving on the hotel. If you have the time, the ferry is recommended for the views to the islands.

Traveling end of July. Days should still be long.

I was very hesitant in taking the overnight ferry from Tallinn to Stockholm until many Fodorites strongly recommended it. Turned out to be one of the highlights of my 15 night trip. I believe we were on the ferry on a Tuesday night, and the staff commented on how "empty" it was... I would say less than 100 of us on the ferry total. The dinner buffet was excellent indeed, so much selection, but I didn't really like the breakfast buffet as much.

The archipelago scenery when we got within a couple hours of Stockholm in the morning was amazing...

I would say for a family of 4 it would be much much cheaper than flying since you will pay per cabin, not per person.

@drlaz what'll be the length of days during July?