Ferries are a long-established way to cross the Baltic Sea between Sweden and Finland with a pet, and Tallink Silja is one of the main operators on these routes. Its own guidance sets out several options depending on the ship: a pet-friendly cabin for up to three pets, a kennel on certain decks, or a carrier bag or crate, each priced per pet and charged in addition to your own fare or cabin.

Pet-friendly cabin fees run from around €15–16 per pet one way plus the cabin price, depending on the ship, and kennel fees are generally lower, around €9–16 per cage or pet one way. Each small kennel cage holds one pet, though two smaller pets may share a larger one, and availability is limited, so it's worth booking the pet option at the same time as the ticket itself.

One detail that differs by route: Tallink Silja's vehicle-deck option, where a pet can stay in your car during the crossing, is only available on its MyStar and Megastar ships on the Helsinki–Tallinn route — not on the Sweden–Finland crossings. On the Baltic Sea routes to and from Sweden, plan for a cabin, kennel or carrier instead of assuming the car works as a pet space. Outside a carrier, pets must be leashed on board and muzzled in crowded public areas; a valid EU pet passport or health certificate and microchip are required throughout.