Sounds like a job for @
Lazy Orang
*Cue suit-up sequence*
I'll be honest, I've struggled to find great books on mythology in the past, so I'll be interested in the responses here, too!
(Especially for more niche mythologies, though I know you're mainly asking about Greek and Norse.
) A lot of my mythological knowledge came from just.... general osmosis when I was a kid, from games like Age of Mythology (which, if you love mythology and have any interest in RTS games, is
well worth picking up on Steam), the Atticus book of Greek myths which is definitely a kid's book but I loved back then, and talking about it with my family because I was just interested, followed by finding things on the internet as an adult... none of which is all that useful to you, sadly!
Robert Graves's book on Greek Mythology is actually a really good, really comprehensive one which I'm glad I own, though I find his writing style a bit on the dry side. Another book I loved as a (somewhat older kid) is was
this one (which doesn't go too deep into anything, but that's because it gives you a broad taste of myths from across the world), but... I'm struggling to find it on the internet now!
I've also enjoyed looking at
this YouTube channel... doesn't seem to upload too frequently, sadly, but they do some interesting videos from all sorts of mythologies.
~Lazy Orang, who doesn't believe she's read that Neil Gaiman book, but who loves mythology and has been enjoying his work on Sandman and kind of feels she needs to try it out now.