@variablepulserate We are on a ferry from Helsinki to Stockholm that leaves at 5 pm (Helsinki time) and arrives at 10 am (Stockholm time). Then we will spend the day in Stockholm and then come back over the next night. It is fairly refreshing to be able to sleep before the visiting Stockholm, and the same applies to when we come back home.
And what comes to the hassle, it is pretty non-existent. As both countries are members of the EU, the Schengen area, and Nordic countries1, one just needs to have the boarding pass with them. Also, the Covid restrictions are pretty relaxed nowadays, so there is no hassle with that either.
Should one wish to travel to Tallinn instead, then there is a bit more hassle due to different regulations. IIRC, one would need s valid ID to be able to enter the ferry. But then again, that trip across the sea will take only a couple of hours, so one will be in Tallinn on the same day even though the ferry would leave in the evening.
// @matigo
There has been constraint-free travel between the Nordic countries well before Schengen or EU.