How to get the Secret of the Cedars shrine quest
Speak with Clavia in Hateno Village, behind the Kochi Dye Shop. She’ll tell about a shrine and reference three cedar trees on top of a mountain. Your job is to make your way there (and eventually to Tahno O’ah shrine).
How to find the Secret of the Cedars shrine quest’s shrine
Tahno O’ah shrine is northeast of Hateno Research Lab. Look at the cedar trees sitting on the mountain, and line them up. Then travel to the far eastern end of that line. Tahno O’ah shrine is hidden behind a rock wall. Use remote bombs to reveal its location. (And use the gallery above to orient yourself.)
Inside, you’ll find Climbing Boots, which allow you to climb faster.