The city lay before Amara and Kael, a silent testament to a world that once was. The glass structures, now frosted over with the passage of time, reflected the faint glow of the bioluminescent shell, casting eerie shadows in the murky waters. Coral had claimed the city as its canvas, painting every surface with vibrant hues of life amidst the desolation.

They swam through what must have been a grand boulevard, flanked by towering edifices that stretched towards the surface far above. Schools of fish darted between columns and arches, the only signs of movement in this submerged metropolis.

Amara's heart raced as she imagined the city in its heyday, bustling with life, the air filled with the hum of conversation and the clatter of commerce. Now, only the soft melody of the shell filled the silence, a haunting reminder of what had been lost.

As they ventured deeper, they came upon a central plaza, dominated by a statue of a figure holding aloft a sphere that seemed to symbolize the sun. Around the base, inscriptions in a language that had not been spoken for centuries told stories of a society that thrived on the power harnessed from the very star that gave life.

It was here, in the shadow of the monument to the sun, that they found it—a data recorder, half-buried in sediment, its surface encrusted with barnacles. Kael carefully pried it loose, and they watched as it flickered to life, its screen a patchwork of static and images.

The recorder spat out fragments of a song, the same melody that had led them here, but now accompanied by words in a haunting harmony. It spoke of a time when the city had mastered the secrets of the sun, of a technology that had promised an era of endless energy.

Amara listened, her mind racing with the implications. This was the lost recording, the voice of a civilization that had reached for the stars only to fall into the abyss. The song was a legacy, a message from the past that held the keys to the future.

They knew they had to return to the surface, to share this discovery. But as they turned to leave, Amara's gaze fell upon the sphere in the statue's hands, and she realized that the city's secrets were far from revealed.