If you go back sixty-four generations, to the time of the Romans, the number of people on whose cooperative efforts your eventual existence depends h… - Bill Bryson

A friend Alan and I ended up in an Outback pub in a place called Daly Waters and apparently, he says, in the course of this very lively evening we spent there I offered to do a house swap with a family from Korea. We weren't sure whether they were from North Korea or South Korea.

It is a slightly arresting notion that if you were to pick yourself apart with tweezers, one atom at a time, you would produce a mound of fine atomic dust, none of which had ever been alive but all of which had once been you.

The Opera House is a splendid edifice, and I wish to take nothing away from it, but my heart belongs to the Harbour Bridge. It's not as festive, but it is far more dominant – you can see it from every corner of the city, creeping into frame from the oddest angles, like an uncle who wants to get into every snapshot. From a distance it has a kind of gallant restraint, majestic but not assertive, but up close it is all might. It soars above you, so high that you could pass a ten-storey building beneath it, and looks like the heaviest thing on earth. Everything that is in it – the stone blocks in its four towers, the latticework of girders, the metal plates, the six-million rivets (with heads like halved apples) – is the biggest of its type you have ever seen. This is a bridge built by people who have had an Industrial Revolution, people with mountains of coal and ovens in which you could melt down a battleship. The arch alone weighs 30,000 tons. This is a great bridge.