Gathering of The Fifty Major Nations!

He was already told by Apollo that the Echoing Tower was called such because of this resounding periodical heartbeat.

It was also the main reason why everyone assumed that the stone of reality was the heart of an ancient creature.

KAAAAA-THUUUUMB!!!

As they got closer to the tower, the thundering heartbeats became louder while the tower started to come into the picture.

After a few moments, The tower stood before them, a colossal structure of pitch-black material that absorbed the light around it, giving the impression of a void in the shape of a tower!

It resembled a gigantic cylinder with tree-like branches extending everywhere, defying any natural order or pattern. 

On these branches hung chaotic portals, swirling with colors that seemed out of place. These portals pulsed with an eerie light, as if breathing, synchronized with the heartbeat that had startled them.