Read it through once

We rode on asses and mules up the steep, narrow streets and entered the subterranean galleries the English have blasted out in the rock. These galleries are like spacious railway tunnels, and at short intervals in them great guns frown out upon sea and town through portholes five or six hundred feet above the ocean. There is a mile or so of this subterranean work, and it must have cost a vast deal of money and labor. The gallery guns command the peninsula and the harbors of both oceans, but they might as well not be there, I should think, for an army could hardly climb the perpendicular wall of the rock anyhow. Those lofty portholes afford superb views of the sea, though. At one place, where a jutting crag was hollowed out into a great chamber whose furniture was huge cannon and whose windows were portholes, a glimpse was caught of a hill not far away, and a soldier said: