You'll need to collect enough Silica (5) and Giant Feathers (20) to upgrade your Power of Raven's endurance. Silica is gained from Raiding Mylna locations, while the video below will show an easy spot to farm Giant feathers. With the upgraded duration, you can reach the Muspelheim Monoliths (floating red rocks) by flying to them from viewpoints and other highpoints around the map.