Secret of the Cedars
Note: This Shrine Quest is optional. It is entirely possible to discover the Shrine without ever activating this quest. If that happens, you will simply autocomplete this Shrine Quest when you receive it.
Talk to Clavia during the day at Hateno Village. She is standing on a dock behind the armor dye shop and will point out to you three cedar trees, plus a strange riddle she once read about.
Fast travel to Hateno Ancient Tech Lab and then pin the little landing shown in the screenshot above. It is west of Afromsia Coast and east of Madorna Mountain. Paraglide towards the mountainous area from the lab and put on some warm armor.
Once you reach the landing, head west until you see a bombable, cracked wall. Bomb it and the Tahno O'ah Shrine will be revealed. Activate the Shrine to complete this Shrine Quest.