Tenojinn

Tenojinn (天の寺院 Te No Jinn, literally meaning "Heaven's Temple of the Origins") is a secret and ancient temple created when Skypiea was created. It is the secret of Shandora, and records all of history in books known as Seisho's. The first and only currently known level of the Temple is a library containing thousands of Seisho's. The most current Seisho was written by Tenshi, telling the story of the Birkan Uprising.

History
When the Skypiean's, Shandorians and Birkans descended to the Earth, the Shandians built the Tenojinn in secret as their most cherished earthly treasure. It was used to record all of the secrets, people and history that was significant to the White Sea. It is thought to be the ultimate source of knowledge and was kept hidden for a millenia, recognized only as the myth, "Secret of Shandora".

Most recently it was discovered by Tenshi, the earth's greatest swordsman and philosopher. He kept it hidden from everyone and was the only person  who knew of its existance during his life. Tenshi was greviously injured during the events of the Birkan Uprising and likely could've preserved his life. But instead he felt it of great importance to record this in the current Seisho. The Temple showed him the truth of the Birkan rising, and he recorded it as he died. He lied on his deathbed, a chair holding the Seisho, laying in eternal sleep for someone to find him and the truth he held.

Tenshi used his Devil Fruit ability to split his soul and merge it with a pirate by the name of Clive. This pirate Captain used Tenshi's wisdom to find the Temple and read the truth of the Birkan Uprising. He then used this knowledge to end the War happening in the Upper Yard.