Quicksand

4th-level conjuration
Casting time: 1 action
Range: 60 feet
Target: 20-foot cube within range
Components: V S
Duration: Concentration, up to 1 hour
Classes: Sorcerer, Warlock, Wizard
Subclasses: --

This spell turns the ground of a 20-foot cube you can see within range, into a deadly vat of quicksand for the duration. The quicksand is difficult terrain. When a creature moves more than 10 feet per turn in the quicksand it must make a Strength saving throw. On a failed save it suffers one level of exhaustion.