Akkala Citadel Ruins Summit Cave can be reached from within a room in the Akkala Citadel Ruins.
Cave Location
At the Akkala Citadel Ruins, you will find a room that has stones blocking the doorway. However, if you go around the corner from that door, you find a small opening at 3282, 1495, 0414 that you can crouch to get into. From there, you can fall into the hole to enter the Akkala Citadel Ruins Summit Cave.
Cave Features
Within Akkala Citadel Ruins Summit Cave, you will find one of Misko's treasures: the Fierce Deity Armor.
Bubbulfrog Location
Break the wooden crates at the side of the room and crouch to go through the small tunnel. You will find the Bubbulfrog in this hidden room.