"I can actual answer your first two questions in one. The cairn, as far as anyone can tell,  is a fairly straight, if long, passage with several inlets off to the sides. This leads to a sarcophagus in the back chamber in a circular room. Most people won't go into the hall though, as a there is a persistent whispering that chamber and they believe it to be a ghost. I have yet to see any evidence suggesting there to be truth behind that. Anyhow, I am convinced the sarcophagus is actually a false tomb, and that the real one is hidden somewhere deeper within the cairn. As to dangers, I'd certainly expect vermin to have moved into the area, perhaps some of great size even. Tremors are also occasional in the area, so it is possible that creatures from the depths of Khyber have made their way in through the cracks. Centaurs and owlbears are known to live deep in the forests, but they rarely come this close to town and I expect that they would have little interest in the burial mounds of ages past."