I just remembered a passage from the Marquis De Sade's "120 Days of Sodom" that seems appropriate (well, not "appropriate",
, but relevant at ant rate). The relevant portion of passage in question details the secluded fortified complex constructed by the protagonists of the story in order to escape investigation and prosecution for... well, for pretty much every other thing that they do in the course of the novel... and which resembles a fortress mode fortress in some of the details of its design.
I've edited the excerpt to remove the overt refrences to perverted acts and other flagrantly NSFW material because, as I previously stated, they are not the relevant portion of the passage in question. HOWEVER, given the original author of the passage in question, i've probably managed to miss something...
...you were warned...
...But the moment has come to give the reader a description of the renowned temple appointed for so many luxurious sacrifices throughout the projected four-month season. He will observe with what great care they had chosen a remote and isolated retreat, as if silence, distance, and stillness were libertinage’s potent vehicles, and as if everything which through these qualities instills a religious terror in the senses had necessarily and evidently to bestow additional charm upon lust. We are going to picture this retreat not as once it was, but in the state of embellishment and yet more perfect solitude that resulted from our four friends’ efforts.
To reach the place one had first to get to Basel; at that city you crossed the Rhine, beyond which the road became steadily narrower until you had to abandon your carriage. Soon afterward you entered the Black Forest, you plunged about fifteen leagues into it, ascended a difficult, tortuous road that, without a guide, would be absolutely impracticable. By and by you caught sight of a sinister and mean hamlet of charcoal burners and gamekeepers; there began the territory Durcet owned, and the hamlet was his; as this little village’s population was composed almost entirely of thieves or smugglers, Durcet easily befriended it, and his first order to the inhabitants was expressly to enjoin them under no circumstances to allow anyone whomsoever to pass on toward the château after the 1st of November, the date by which the entire society was to be assembled in it. He distributed weapons to his faithful vassals, granted them certain privileges they had been long soliciting, and the barrier was lowered. That done, and the gates tightly sealed, one will see by the following description how difficult of access was Silling, the name Durcet’s châteu bore.
Having passed the village, you begin to scale a mountain almost as high as the Saint-Bernard and infinitely more difficult to ascend, for the only way to reach the summit is by foot; not that the route is forbidden to pack mules, but such are the precipices which everywhere border the one so very narrow path that must be followed, that you run the greatest danger if you ride; six of the mules used to transport supplies and food perished, taking with them two laborers who had though to mount astride them. Five full hours are required to reach the top of the mountain, and there you come upon another extraordinary feature which, owing to the precautions that had been taken, became a new barrier so insurmountable that none but birds might have overcome it: the topographical accident we refer to is a crevice above sixty yards wide which splits the crest into northern and southern parts, with the result that, after having climbed up the mountain, it is impossible, without great skill, to go back down it. Durcet had united these two parts, between which a precipice fell to the depth of a thousand feet and more, by a fine wooden bridge which was destroyed immediately the last of the crew had arrived, and from this moment on, all possibility of communicating with the Château of Silling ceased. For, cross the bridge and you come down into a little plain about four acres in area; the plain is surrounded on all sides by sheer crags rising to the clouds, crags which envelop the plain within a faultless screen. The passage known as the bridge path is hence the only one by which you may descend into or communicate with the little plain; the bridge removed or destroyed, there is not on this earth a single being, of no matter what species you may imagine, capable of gaining this small plot of level land.
And it is in the center of this flat space so well surrounded, so solidly protected, that one finds Durcet’s château. Yet another wall, thirty feet high, girds it; beyond the wall a moat filled with water and exceedingly deep defends a last tall and winding enclosure; a low and strait postern finally leads into the great inner court around which all the living quarters are built, and they are very capacious, very well furnished thanks to the arrangements latterly concluded; one discovers a long gallery on the first floor.
....
But depravity, cruelty, disgust, infamy, all those passions anticipated or experienced, had erected another locality whereof it is a matter of urgency that we give the sketch, for the laws essential to the proper unfolding of our tale demand that we depict it with thoroughness now.
A fatal stone there was which, cunningly made, could be raised from below the step of the altar in the little Christian temple we discerned from the gallery; beneath that stone one beheld a spiral stairway, very narrow and very steep, whose three hundred steps could convey you down into the bowels of the earth, to a kind of vaulted dungeon, closed by triple doors of iron, and in which was displayed everything the cruelest art and the most refined barbarity could invent of the most atrocious, as much for gripping one with terror as for proceeding to horrors. And there below, what tranquillity! to what degree might not the villain be reassured who brought his victim there! What had he to fear? He was out of France, in a safe province, in the depths of an uninhabitable forest, within this forest in a redoubt which, owing to the measures he had taken, only the birds of the air could approach, and he was in the depth of the earth’s entrails. Woe, a hundred times woe to the unlucky creature who in the midst of such abandonment were to find himself at the mercy of a villain lawless and without religion, whom crime amused, and whose only interest lay in his passions, who heeded naught, had nothing to obey but the imperious decrees of his perfidious lusts. I know not what will transpire in that nether place, but this I may say without doing our tale a disservice, that when a description of the dungeon was given the Duc, he reacted by...
...Everything being ready at last, everything perfectly disposed, the subjects installed, the Duc, the Bishop, Curval, and their wives ... set off (Durcet and his wife, together with all the rest, having arrived beforehand, as we have previously noted), and not without infinite difficulty, finally reached the château on the evening of the 29th of October. Immediately they crossed it, Durcet had the bridge cut. But that was not all: having inspected the place, the Duc decided that, since all the provisions were within the fortress, and since therefore they had no need to leave it, it were necessary, in order to forestall external attack, which was little dreaded, and escapes from within, the possibilities of which were less unlikely, it were necessary, I say, to have walled shut all the gates, all the passages whereby the château might be penetrated, and absolutely to enclose themselves inside their retreat as within a besieged citadel, without leaving the least entrance to an enemy, the least egress to a deserter. The recommendation was put into effect, they barricaded themselves to such an extent there was no longer any trace left of where the exits had been; and then they settled down comfortably inside. [/b]