Astin's Cheshire Passage

You weave magic through your body, causing your form to become momentarily fluid-like. For the duration, you can move through spaces as narrow as 1 inch wide without squeezing, and doing so doesn’t reduce your movement speed.

Additionally, you have advantage on Dexterity (Acrobatics) checks made to move through or escape tight spaces, and you ignore nonmagical difficult terrain.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, you gain resistance to bludgeoning damage for the duration. However, whenever you take bludgeoning, piercing, or slashing damage from an attack, you are pushed 5 feet in a direction determined by the attacker.