The coastal Chinese city of Zhuhai is linked to Hong Kong by a showy piece of infrastructure:
a 55km (34-mile) bridge and tunnel, the largest sea crossing of its kind.
Some Hong Kongers use it to visit Chimelong Ocean Kingdom,
a theme park featuring a whale shark, rollercoasters and a hotel shaped like a spaceship.
Others are motorists with a more mundane purpose.
They travel to Zhuhai to fill up their tanks with petrol,
available at a big-enough discount to make the drive worthwhile.
The mainland's petrol-price formula smooths out the international market's ups and downs.
As such, it is one of the ways China's government is shielding citizens
from the effects of the war in Iran,
which has trapped oil tankers on either side of the Strait of Hormuz
and damaged energy infrastructure in the Gulf.
There are plenty more.
As an emergency measure, China's planning agency has banned exports of refined products
including petrol, diesel and jet fuel.
The country's small, independent "teapot" refiners, clustered in Shandong province,
are busy processing Iranian crude, which is still allowed to pass through the strait.
And if the war drags on, China may also dip into its vast strategic reserve of oil,
which it diligently topped up when oil prices were low last year.
"This is China's nightmare," said Lindsey Graham, an American senator, earlier this month.