The darkness of dusk encompasses a location you choose within range. Until the spell ends, a 30-foot-radius, 40-foot-high cylinder of complete magical darkness appears there. 

When the cylinder appears, each creature in it must make a Constitution saving throw, taking 6d8 necrotic damage on a failed save, or half as much damage on a successful one. A creature must also make this saving throw whenever it ends its turn in the cylinder.

If you’re within 60 feet of the cylinder, you can move it up to 60 feet as a bonus action on your turn.