Ancient Prison

It is a bizarre and troubling place. The narrow corridors with edges like blades of steel, cutting you at one wrong movement. The dark, the smell. The very sounds it makes are like those of hell itself, the echoes of endless torture. One cannot help but wonder what kind of twisted civilisation would build such a thing, and how humane we are in comparison.

Truth be told, it is hard to notice the place even should you be right on top of it. Buried under a layer of sand and part-submerged by the island shore, this strange metal construction has puzzled the scholars for the better part of the decade. It is large, the size that would make fit for a noble's mansion, but in a strange shape - long and narrow. Parts of the construction are broken off, and the interior is extremely confusing. Long narrow corridors all look the same and many people got lost inside, telling stories of the intimating feeling of being stuck in an endless loop. There is no light, and the rooms are more like cells - small and with barely a bed inside, the entrance clearly locked shut by a semblance of a door.
Based on these factors, as well as the general impression the structure has left on all of its explorers, the main theory was formulated. The structure was in fact a prison, a place meant to intimidate and haunt the less honourable members of society. A man-made hell on earth. However, a group of scholars have recently put forward a much different idea. The creators of this structure were clearly very skilled, perhaps even more so than we are nowadays. It also required an overwhelming amount of metal to build, a reason why the structure is now actively guarded against looters and pirates. Why would such an advanced civilisation stoop to needless brutality? Does the shape of the structure not resemble, albeit in some cruel and twisted way, that of a giant warship?