[codethief]

> Here in Japan, some remote islands, you can travel overnight boat.

I'm sure there are many overnight ferries all over the world and I can't say I have traveled with many, but one I can recommend is the overnight ferry from Ziguinchor/Senegal to Dakar – it's reasonably priced (for a foreigner), and the cabins are very comfortable and even include a shower!

Meanwhile, the 3-day ferry from Puerto Montt (central Chile) to Puerto Natales (Patagonia) is very expensive (> 500 USD per person for the most basic cabin) and very unreliable (expect last-minute cancelations).

[abecode]

Corsica to Marseilles has an overnight ferry, at least back in 2000, but I don't think it's has sleeper cabins, more set up like an overnight flight, but a big cruise ship form factor. Instead of cabins they had space for cars. They had the option of getting a ticket without a seat so you just roam around the boat and find an open space, including outside on the decks.