Something that is somniferous makes you feel sleepy or helps you sleep.
Things that are somniferous are usually good because they help you relax and rest.
Examples:
The somniferous music helped me fall asleep.
The somniferous scent of lavender filled the room.
She drank the somniferous tea before bed.
The somniferous effect of the warm bath was very strong.
The somniferous power of the bedtime story was amazing.
The somniferous sound of the rain put me to sleep.