All the signs were telling them in no uncertain terms that the Dark Emperor's tomb was highly possibly located beyond the Heaven's End Cliff, and all the members of the Twelve Palaces that had been mercilessly murdered and their families rooted out had actually mapped out the terrain at the bottom of the Heaven's End Cliff.
Otherwise, with the overwhelming might of the Twelve Palaces, it was impossible that they were still unable to find the Dark Emperor's tomb if it had been anywhere else.
But if the place was completely filled with traps and covered completely in impenetrable fog, a complete and precise map would be needed to locate the place.
