What are some mysteries which will never be in solved at al

It is possible that we cannot say a mystery cannot be solved because eventually crucial evidence might come forward, such as death-bed confessions.

For example the Bogle-Chandler mystery was potentially solved 45 years later.

At a party on New Years Ever 1962, Dr Gilbert Bogles wife went home early. Bogle and Margaret Chandler left later. Their naked bodies, covered with bark were found on New Years Day in a park. No cause of death was ever established.
40 years later a man came forward saying his friend who had just died, told a story of exercising his greyhounds at dawn and finding the 2 naked bodies, and covered them with bark for modesty and then went home without telling anybody.
Others then came forward saying that a swamp in the park next to the grassy hollow where the bodies had been discovered, occasionally released hydrogen sulfide gas which is heavier than air and very toxic.

DNA is a powerful tool which can reach back through the years, shining a light on a cold case.

Geothermal Energy.

The structure was created as you say thousands or millions of years ago...

Then, the Atlanteans built their capitol city on top of it to use the Geothermal Energy to heat their homes and water, while at the same time, using the "lower altitude" rings to create their ringed waterways...

When the great cataclysm occurred 12,000 years ago, the ice age quickly ended resulting in rapid glacier melting and global storms, causing multiple floods and drastic sea level rise, which resulted in tidal waves coming inland and blasting away all the buildings off of the Richat Structure...

When the waters "receeded" and dried up, it left behind all the salt that can now be seen.

Why do you think that her brother killed her?

I've been to Santorini. Yes, I heard that theory too (that it was Atlantis).

You're an idiot troll.

He was talking about his own account. 

Another dumbass troll account.

Keep it up!