As I grow into my job I am starting to find more ways of being more efficient and spending less time of things I have spent much more time on in the past. The end result is more downtime

Yes I know I probably should be seeking for other things to do that result in busy work but there is only so much that can be done on slow days like Sundays specifically.
I thought as an option I would be able to remote to my computer at home from work and use my masses of study material I have on my computer. Turns out I can't establish RDP from work to home, I'd assume its being blocked from my company firewalls/ etc. So in turn I am looking for other ways I can use my time. Sundays are especially slow and I want to use some of my downtime on these days to study for my upcoming exams.
Anybody know of any free content available online that is legitimate that can be used for studying in my downtime? Please DO NOT suggest a brain **** site, I am very against these and I know many people here are as well. I am looking for actual publications or documents written by reputable sources that will aid in my downtime / study efforts.
Thanks!