Ethereal Step

When you cast this spell, a magical force is created under your steps allowing you to walk and crawl on air as if there were a platform underfoot. You may ascend and descend as if climbing stairs, however, doing so is treated as rough terrain. 

You may ascend as high as you wish, however, when you start your turn over 30ft in the air from the ground you must roll to hold concentration on the spell. If you're over 60ft from the ground, you must roll to hold concentration with disadvantage. While out of combat, these roles are done every 5 minutes. The DC for this concentration roll equals 10 + 1 for every ten feet above the ground.