This page explains how to find the Mijah Rokee shrine.
How to Reach the Shrine
You might want to bring wood and flint with you before you look for this shrine. You might also want to bring some stamina-boosting foods. (It can be done without any stamina boosts or stamina wheel upgrades, but it is difficult.)
Go east from Shae Loya Shrine, then when the road goes south and you see a wooden sign, avoid the person standing there (secretly a Yiga assassin) and go south up the slope. This is Washa's Bluff. Go to the southern end of Washa's Bluff and you can see Kass the Bard on top of the tallest flat-topped tree.
If it is raining, you might want to start a campfire and sit until later.
When it has stopped raining, climb to the top of the shortest of the trees near Kass's tree. From there, jump to the trunk of the next-tallest tree and climb to the top, then jump to the trunk of the tallest tree and climb to the top. Be careful to make sure that Link is climbing upward and not at an angle. Stop from time to time to make sure that Link is still going the right way. If you have low stamina, do a jump just before your stamina runs out, and you might make it. Also, by jumping from tree to tree, if you do fall, you might land on the top of the previous tree.
At the top, talk to Kass to start the "Under a Red Moon" shrine quest. You can also read the nearby book to find out where else in Hyrule you can find Kass.
The clue says to stand on the pedestal during a Blood Moon "bare / With nothing between you and the night air." In other words, during a Blood Moon, stand on the pedestal and remove all armor.
If there will be a Blood Moon tonight, the pedestal will start glowing orange at 9PM, and will stop glowing at 1AM. Stand on it while it is glowing, with no armor equipped (weapons are fine), and the pedestal will go from orange to blue, and the shrine will appear.
A normal Blood Moon can happen if you have played the game for about 3 hours (real-world time) and have spent about a week in the game (not counting time in the + or - menus or talking to NPCs, etc.) Then once you sleep or sit by a fire, a Blood Moon can occur if the moon will be full that night.
You can talk to Hino at Dueling Peaks Stable (near Ha Dahamar Shrine) during the day to find out what tonight's moon will be. If he says "I'm getting that feeling again", then tonight's moon will be a Blood Moon. The moon phases, in order, are full moon (or Blood Moon), "a little smaller than last night", third-quarter moon, 26th-day moon, new moon crescent moon, seven-day moon, and 13th-day moon.
If you want to wait for the Blood Moon, go to Shae Loya Shrine, preferably some time around noon or at least before 9PM, then go south to the pedestal on Washa's Bluff. Stand on the pedestal and unequip all armor, then wait. Or start a campfire with wood and flint (or flame weapons, etc.) and wait until night. If there will be a Blood Moon tonight, the pedestal will glow orange at 9PM, and will stop glowing at 1AM. Unequip all armor and stand on the pedestal when it is glowing orange.
About the Shrine
This is a Modest Test of Strength shrine. The Guardian Scout wields a Guardian Sword+ and a Guardian Shield+.
The chest in the shrine contains a Frostblade.