"It's an enormous cave made out of meat," John retorted, still refusing to turn around and see if Sherlock was making an approving face at him. "Of course it would take something massive to build it. Or grow it. However it was formed." He still wasn't convinced that it wasn't a hallucination cooked up by his dead or dying mind, though Sherlock's impossible certainty that it isn't makes John's belief feel much less sturdy.

The lights are still leading them upward, which John hopes is a good sign.