The weight of air

Once, on a school trip which had taken a coach full of children and three teachers to a cave, which had been smaller than her preconception had painted it, she had been unable to breathe. She had been intensely aware of the mass of rock above them. It had seemed an impossibility that they should not be crushed. The fact that the cave had been there for hundreds - thousands - of years somehow made its imminent collapse more rather than less likely.

And now, under the sheer expanse of seaside sky, bigger than the constrained sky of her city, she felt the same pressure. Too much air to breathe.