I loved listening to Isaac Arthur's youtube videos, and it helps a lot in falling asleep(then I discovered low dosage melatonin).

His voice is so calming and re-assuring and the background music also helps.

The O'Neill cylinders series never failed to make me sleep -- I could imagine myself living in such a neat space, floating in the middle of such a cylinder, producing large amounts of food, the world's problems far away, and boom, I'm asleep.

I think I used to fall asleep like this when I was kid imagining I was travelling in captain Nemo's submarine.