It was not very accurate to say that he did not see it, because Li Yao had been dizzy since he 'fell from the sky' and did not see the inside of the entrance clearly.
However, according to Li Linghai's experience and the memory pieces of Black Star Emperor Wu Yingqi, there should be an almost perfect ball of mercury inside the tomb of the Supreme Emperor, which was floating in the sky like an eternal moon. The Supreme Emperor had built a forward base around the 'entrance', and so had Li Linghai. He had stationed his camp right below the entrance all the time. Therefore, Li Yao should have been able to see its coordinates when he entered the tomb.
Of course, the precise coordinates of the Tomb of the Supreme Emperor were in the depths of the four-dimensional universe. Amid the raging tides, its entrance appeared and disappeared in the three-dimensional universe. Chances were that it had already 'disappeared' in the three-dimensional universe.
