Much of the Underhive is unexplored or inaccessible and amongst the ruins lie factories, machines, stockpiles of raw materials and stores of artefacts buried millennia ago. Sudden structural catastrophes are not uncommon in the lower parts of the hive, so it is easy to imagine how a collapsed dome could be buried along with its inhabitants. Over time the dome will be forgotten, wastes leak in from above, and layers of hive dust pile on top of the ruins. All this can remain untouched for centuries, perhaps for millennia, until erosion or a hivequake open up a small crawlhole into the ancient dome.
When a tunnel into a new area is discovered it becomes a magnet for fortune hunters. Any attempt at secrecy can only succeed for a short while, and soon the dome will be teeming with rivals. Inevitably there will be battles over the spoils, and the victors will carry away the choicest items for themselves.
Archeotech is the term given to ancient finds of technical artefacts. The richest source of archeotech is lost domes, but it is possible to find old machines at the bottom of any deep layer of hive debris. The value of an item depends very much on what it is. Old rusted machinery is only good for scrap and will have to be sold for the value of the metal it contains. Isotropic crystal fuel rods, on the other hand, remain good so long as they are unused, and can be traded for a good price.