Yeah Finland is in the EU, but doesn't use the Euro, most Scandinavian countries have their own currency and are pretty cashless for the most part. The US is so big that you don't need a passport to get sun and ski, mountains and beach a bit like the EU. But we're on an island here so always needed passports to travel to any country except the UK. Buy if you're in the Schengen area (where Finland is, you don't need passports to drive or fly to other countries also in shengen area) more so just for ID, so a driving licence would probably do for that. But Finland borders Russia, so you'd need a passport and visa to go there, but there's probably travel advice against it for US citizens (the norm). But you could drive to Norway/ Sweden/ Denmark, etc or any other nearby country with a land bridge, without a passport. But Iceland, UK, Ireland you'd need your passport to travel from Finland as their islands. Enjoy the trip and safe travels. Never been to Finland, but sounds cool.