If you've already watched everything you want to watch on Netflix, it might be time to subscribe to CuriosityStream. The streaming service is essentially the Netflix for documentaries, and includes unlimited access to thousands of documentaries and educational shows.
A bargain at its usual $20 per year, they just dropped the price to $12 per year, or $42 if you want to watch in 4K. That includes access to the app on your favorite TV streaming device, and even offline downloads on your phone or tablet.
1 Year Subscription To Curiosity Stream | $12 | Normally $20