I think podcasts are underrated, especially episodes with book authors. If a podcast has a knowledgeable host, then she can add context that you would miss on your own. You can also get the main takeaways of a book in an hour.
EconTalk: listening to EconTalk might be my highest ROI activity. I will add some of my favorite episodes soon, but until then Rob Wiblin has a great list of recommended episodes
Rationally Speaking: listening to Julia Galef might be my second highest ROI activity. Rationally Speaking may be inactive as of 2023, but the existing episodes are great