Cruise Stockholm to Helsinki

Do you mean a ferry? There is regular overnight ferry service between the two cities. The ferries are more like small cruise ships in the restaurants, nightclubs and shopping. But it's not a "cruise." And many locals do this for some fun and tax free shopping.

There are two ferry lines: Silja and Viking. Both are perfectly good though Viking has a reputation (not sure if deserved) as being a little more of a party boat. I've taken the Silja ferry and it was great.

This is an excellent idea. Regardless what you call them (I think they are closer to cruise ships -albeit smallish ones- than ferries), they are an easy way to see a fascinating city and cover two nights of lodging at a very reasonable price. And you get to sail through two archipelagos which are beautiful. It's very easy to get around Helsinki for the day. we took the Silja line at the advice of our Swedish friends.

p.s. You can also take an overnight cruise to Tallinn, Estonia, another fabulous city.

I've taken the Silja and had a great time. Definitely do the buffet dinner - it was a good treat. I would also recommend a room with a window.