Most people who travel to Hokkaido go by plane or by overnight sleeper train, but there is another option. Mitsui O.S.K. Lines run large 'Sunflower' car ferries between Oarai, Ibaraki and Tomakomai, Hokkaido. This is a good option if you have more time than money, or if you want to take your own vehicle (car or motorcycle).
With our own car, my husband and I booked a deluxe room – twin beds, TV, small table & chair, and a unit bath/toilet. The room was simple, but clean and comfortable. Other accommodations onboard include standard rooms for four – tatami or two bunk beds, casual rooms with four bunk beds, and large, carpeted economy rooms for budget travelers – who sleep side-by-side on the floor. The ferries themselves are older and very basic. Most of the space is occupied by vehicles and cargo. The upper decks hold passenger rooms, TV lounges, a free mini movie theater (playing 'Tora-san movies), a kids' play space, a restaurant, a game center, a gift shop, vending machine corners, and large, segregated baths. There is also a deck where passengers can go to get some fresh air.
On our trip, almost all of the passengers were truck drivers, young Japanese soldiers, and retired budget travelers. Passengers have the option of bringing food onboard or eating in the restaurant. The dinner buffet (1900 yen) had a tasty selection of simple Japanese, Chinese, and 'Western' items and was served from 18:00-19:30. Beer and wine was available for purchase. Breakfast (1,050 yen) was served from 7:30-9:00 and was mostly Japanese. Lunch (800 yen) was served just before arrival, from 12:00–13:00, and was a minimal 'buffet' of two Japanese curries, two pastas, a simple salad, and a clear soup. Purchase the discounted two meal coupon for 2,400 yen. Dinner and breakfast were quite good, but have curry for lunch as the pasta is substandard.
The ferry is large and follows the coast. But it is a rocky ride, especially if the weather is bad. There is almost nothing to do onboard, so we spent most of our time sleeping or laying in bed reading or watching TV. There isn't much on the TV, but it is possible to rent DVDs onboard, although the selection is limited. Cell phone service was spotty.
I was most impressed with the public baths. They were spacious, clean, and it was wonderful to sit in the hot water while looking out at the ocean through large picture windows. As almost all of the passengers were male, I was alone both times I bathed.
The 'Evening' ferry departs at 18:30 from Oarai, Ibaraki, arriving at 13:30 the next day in Tomakomai, Hokkaido. The return 'Evening' ferry departs Tomakomai at 18:45, arriving in Oarai the next day at 14:00. There is also a 'Night' ferry that departs Oarai at 1:45am, arriving the same day at 19:45. Then, leaving Tomakomai at 1:30am, arriving in Oarai the same day at 19:45.Be aware that Tomakomai is not near Sapporo, so if you are not bringing your own vehicle, a sightseeing package ticket might be a good idea. It is also important to note that Oarai is about an hour and a half north of Tokyo - by car or train.