Arena (Short Story)

It was hot, and he was lying on sand, and a rock embedded in the sand was hurting his back. He rolled over to his side, off the rock, and then pushed himself up to a sitting position.
'I'm crazy,' he thought. 'Crazy -- or dead -- or something.' The sand was blue, bright blue. And there wasn't any such thing as bright blue sand on Earth or any of the planets. Blue sand under a blue dome that wasn't the sky nor yet a room, but a circumscribed area -- somehow he knew it was circumscribed and finite even though he couldn't see to the top of it.
He picked up some of the sand in his hand and let it run through his fingers. It trickled down on to his bare leg. Bare?