The only way, except from flying, to access Sweden largest island: Gotland. The boats are ok and bring you over between 2 and 4 hours depending of which Harbour and which type of ferry you travel from with. Västervik is the fastest way and it's also straight over from the main city on the island, Visby. but from here the ferry only operate drmuring summertime and only once a day.
Nobody has to understand why inmidst of the summerseason the ferry does not run for full two days in the middle of the week, whilst all the ferries are fully booked, either from oscarshamn nor västervík.
Destination Gotland fast speed ferries recommended must travel
Comfortable boat. Good that you get a seat with the ticket. Easy to get on. The negative is that the price is perhaps on the high side and the food is not top notch.