The Missing Key to the Lost Temple

The Vesi Tildin, the lost temple, is a mythical structure erected during the first era somewhere in the Sichine Nilne, the forest of the elves. Legends told the temple has three majestic gates, representing the past, the present and the future. Two elven chieftains possess the keys for the past and present gates, while the third key location is unknown.
Only among the elves, some people claim this legend is true: nobody has ever seen the lost temple, thus nobody can confirm three gates are present, nor that the keys possessed by the chieftains open two of them.
Nevertheless, most elves are firmly persuaded the temple exists, somewhere, and that someone will find it at the right time, along with the missing key.

Historical Basis

The only objective truth of the whole story is the fact that two elven chieftains possess two keys. In an ancient poem, often sung by elven bards, it is stated that "the third key will reveal a bright future in the old temple"; this would be a proof for the existence of the missing key. Moreover, on the other two keys are engraved the words "past" and "present", which obviously call for a third key. Most sane people say that the engravings are late additions with the exact purpose of making sense of the legend.

Cultural Reception

Elves are confident about the existence of the lost temple and consider themselves the guardians of the keys: it is their duty to find the missing one and look after them. This sentiment is particularly strong in the tribes possessing the two remaining keys.
They sing many different variations of how the missing key got lost, though most of them feature heroes fighting hordes of demonic creatures.
Sometimes a new key is found and tribes meet to argue about its authenticity, comparing it with the other two and trying it on some known closed gates in ancient ruins scattered throughout the forest. The verifications last often for more than a year. If a key passes all the tests, shamans from various tribes ask the spirits of nature about it or compare its magical energies with the original ones. Until now, they either opened some other lock or were considered to be fake, by a close comparison with the materials or shape of the others, or after a shaman response.