The heavy door turned on its hinges. A fairly spacious cavern appeared before their eyes.
"We must be exactly under Fort Fréfossé," said Beautrelet. "We have passed through the different earthy layers by now. There will be no more brick. We are in the heart of the solid limestone."
The room was dimly lit by a shaft of daylight that came from the other end. Going up to it, they saw that it was a fissure in the cliff, contrived in a projecting wall and forming a sort of observatory. In front of them, at a distance of fifty yards, the impressive mass of the Needle loomed from the waves. On the right, quite close, was the arched buttress of the Porte d'Aval and, on the left, very far away, closing the graceful curve of a large inlet, another rocky gateway, more imposing still, was cut out of
