The North Sea. The Hull crossings to Rotterdam (NL) and Zeebrugge (Belgium) are/have been overnight, about 11 hours, departing at 8 pm. They’re not quite this well appointed, but they’re certainly set up to cater to those who’d rather stay up all night as well as those who just want a cabin to sleep in.

There are short ferry routes from Britain to the continent (the 90 minute or so crossings of the straits of Dover) but pretty much all of the other routes are long enough to have overnight crossings with beds and bars and a captive audience for anything they think they can make money out of.