Ferry from Riga to Stockholm goes every day. Road lasts 16 hours. Also there are ferries to Germany. To make you trip cheaper - it is necessary to buy tickets beforehead.
Thanks to low cost airlines, which goes from Riga, it is profitably to get to different European cities through Latvia. Options of transit: AirBaltic, Ryanair, ferries.
Riga Passenger Terminal
If you're travelling to Riga with Tallink from Stockholm then you'll arrive here.
Eksporta, 3a (+371) 67 32 62 0002