Enjoy 'Megastructures'. Dépendent on subject matter, will usually watch this type of doco.
'Air Crash Investigations' is 'homework' to me!
Doco's on usually any Science: Geology, Astronomy, Nature & Natural History, Ancient History, Exploration, Art, I soak-up like a sponge! Really enjoy them. Always have. Can learn so much, & I find them very interesting.