The dungeons below are protected by a powerful curse. The Death Swarm will try to consume your soul. Heed the mini-map and avoid its oppressive clutch. The circle will slowly move closer towards the white circle indicated on the mini-map. If you are caught in the red zone you will slowly start taking 1 damage per second. However, if you are in the last circle and cannot find a portal in time before the circle fully closes, then you will instantly die.
Check individual Dungeon page to see their death swarm timings.