Once, in a bustling coastal town named Seaview, lived an ardent lighthouse keeper named Elias. Loved by the town-folk, Elias embraced an admirable sense of duty towards safeguarding the seafarers from treacherous storms. His intriguing fascination for the sea was as boundless as the ocean itself.

One grim night, amidst a monstrous storm, Elias spotted a floating bottle holding an ancient treasure map during his usual patrol. Along with the map, a mysterious note mentioned 'Explore the unseen world of Hitherside.' Elias's curiosity knew no bounds. He decided to embark on his adventure to seek this mysterious world.

More eager than ever, Elias ignited the lighthouse and set sail the very next day. But the sea, like a riddling Sphinx, did not provide any easy voyages. At every juncture, the coast pushed Elias into numerous challenges; shark-infested waters, sea storms, and rocky isles tested his spirit. However, Elias, motivated by his relentless courage, did not succumb to the sea's trials but forged ahead.

The pivotal moment arrived when Elias approached a colossal whirlpool, swirling at the mapped location. Unexpectedly, resisting the powerful waves, he navigated his boat into the vortex. Bracing himself for the unknown, Elias plunged into the whirlpool's centre.

A kind of stillness enveloped him, and when he opened his eyes, he was in front of a shimmering portal. Elias's heart pounded with anticipation as he entered the portal. To his amazement, a world of unprecedented beauty unfolded. Fluorescent coral reefs, fish of fantastic colours, giant tortoises, luminous jellyfish, and underwater creatures unknown to mankind surrounded him. He was in the 'Unseen World Of Hitherside.'

Surprisingly, this unknown realm did not lack human life. Adorned with mesmerizing seashells, the ocean floor was home to a tribe known as the Selkies. The Selkies, known for their impeccable magic, transformed from seals to humans. They embraced Elias and treated him like their own, enlightened him with their rich cultures, underwater farming techniques, language, and most importantly, their purpose - 'To protect the ocean and its creatures'.

They revealed the sincere reason behind sending him the map. The Selkies were fretting over an impending disaster triggered by an erupting underwater volcano endangering their marine life. As the humans didn't know about them or Hitherside, the Selkies selected Elias to communicate their plight given his responsibility as a lighthouse keeper and love for the sea.

When Elias returned, he shared the Selkies' harrowing reality with Seaview's inhabitants. Sensitized by the tale, the human community voluntarily offered help. The experienced seafarers and skilled divers of Seaview assisted Elias in employing various methods to divert the lava flow and save Hitherside. They executed the plan just in the nick of time, preventing the catastrophe.

Elias's remarkable adventure not only brought the Selkies and humans together but also increased their understanding of coexistence. Both communities pledged to guard and respect each other's world. This incident sparked a childhood fascination into a lifetime mission for Elias - ensuring the protection of land and sea inhabitants alike. Throughout his life, he served as a bridge between the two worlds and lived up to the promise he made to the Selkies.

As for Seaview, the inhabitants' life remained untampered by the sea's mysterious world. They continued their lives with utmost reverence, holding in their hearts a unique respect for the lighthouse, Elias, and the sacred sea that danced before them.