"Indications that a huge [Alexander-era] tomb being excavated in Ancient Amphipolis, northern Greece, could have a doorway leading to a fourth chamber have not been confirmed by the dig..." Source: Archaeology News Network.
"Archaeologists working in the tomb’s third chamber thought a gap in the wall could lead to a fourth vault but the dig revealed a marble block had been removed from the spot..."
The exacavation of this fantastic tomb has been going on for some time now and there has been a lot of speculation about who might be buried there. The hypothesis at this point is that there might be a fourth chamber hidden under the floor of the third chamber, i.e. that the floor could be a "horizontal sealing wall."
Meanwhile, the Greek Culture Ministry (?) just released the video below showing the third chamber with its mosaic floor and some details of sphinx statue fragments that were recently discovered inside. These are "the head [of one statue?] and fragments of the wings belonging to the two sphinx statues at the entrance of the tomb," according to the Greek newspaper To Bhma.