The three weeks it takes to get from Hong Kong to London by train (on a circuitous route) may seem like a long time - and it is a trip you'd want to do for its own sake - but one advantage the journey has over air travel is that it is not likely to be put in jeopardy by an Icelandic volcano.
Travelling as a foursome forestalls the greatest inconvenience of transcontinental train travel: sharing a cabin with a stranger who might sit too close, eat cuttlefish snacks or snore. Each compartment on a sleeper train, be it in China, Mongolia or Russia, has four beds and a sliding door, so our nuclear family can settle down, click the lock and interact with Chinese cellphone salesmen, Russian farmers and other fellow travellers in the buffet car and in the corridor, on our terms. First-class two-bed cabins are available with table flowers and, it is rumoured, access to a shower - but all that comes at a price.
The line to Beijing is electrified and fast but the view is mostly of rural China: cabbage fields, small houses and sparse, angular trees that look like they've been drawn by a child. There are hardly any trees at all in the vast horizontal views further north, where the train bisects the Gobi Desert and the prairies of Genghis Khan. Here everything seems utterly foreign and Outer Mongolia, as it was known during the Qing dynasty, even sounds a long way from anywhere else. But this journey is really about Russia.
We reach it after midnight and, despite the machine guns and uniforms, the border guards are kinder than warnings suggested. They apologise for the disturbance and smilingly compare our children's faces and passports without waking them.
The next stop is Irkutsk, by Baikal, a freezing cold and improbably deep lake that contains 20 per cent of the world's fresh water. The lake freezes to a depth of four metres in the winter and in the past, tracks were laid across the ice for the train to steam right over.
There's no ice on our visit but a cobalt blue infinity of water that's astonishingly clear and inviting. Legend has it that by dipping a hand into the lake you add a year to your life - brave the waters for a swim and you'll be around for an extra 25 years. I wonder how much you get for a toe, as that is all we manage in water that may not be ice but feels frozen, even in mid-summer.