The Adventurers by Gustave Aimard

Don Tadeo and his friend Don Gregorio were introduced, after exchanging several passwords, into a subterraneous apartment, the entrance to which was perfectly concealed in the wall. The door closed immediately after them; the two men turned round sharply, but all signs of an opening had disappeared. Without taking further notice of this circumstance, which they no doubt had expected, they cast an inquiring glance around them, in order to obtain some knowledge of the locality. The place was admirably chosen for a meeting of conspirators. It was an immense apartment, which must have served for a long time as a cellar, as was made evident by the essentially alcoholic emanations still floating in the air; the walls were low and thick, and of a dirty red colour; a lamp with three jets, hanging from the roof, far from dispersing the darkness, seemed only to render it in a manner visible. In a recess stood a table, behind which a man in a mask was seated, near to two empty seats.

Men enveloped in cloaks, and all wearing black velvet masks, were gliding about in the darkness, silent as phantoms.