Your Options for Getting from Stockholm to Helsinki
There's a 16 hour long ferry connection between Stockholm and Helsinki leaving in the afternoon and arriving the following morning. The Viking Line and the Silja Line ferries both cover Stockholm-Helsinki. The Viking Line offers cheaper cruise prices but uses older ships; Silja Line cruises are more expensive but also offer more elegance. Starting around €40, this is a cheap way to get from Stockholm to Helsinki or back, but not very fast.