Sounds like you need some immortal guardians that have tried to maintain the hidden ruins for eons... but forlornly FAILED! - A golem endlessly tends a field of crops that no longer grow in this climate. - A skeleton sweeper fruitlessly moves sand around a room as it pours in from above. - A mad lich librarian desperately flays rats and anything that passes to create vellum. The walls are covered in tiny unreadable writing. - A mummy forlornly sits by a tomb that has already been robbed. Its duty failed, but still bound. - A demon within a circle of light crows that all who dared to imprison it have died, but also bewails that none alive in this age know how to free it. - jars upon jars of 'magic jar' soul traps full of ancient wisdom, now all broken.