Well, for manhwa with a mythological bent, my immediate answer would be Dokebi Bride. I've been reading it in Korean, but I know all the available volumes are out in English translation. (Unfortunately, everything else I've read myself isn't translated.)
There are other titles that I haven't tried out myself but seen recommended, like Antique Gift Shop and Time and Again (the latter might be more Chinese than Korean though).
Hm...I don't really have any nonfiction recs precisely--to be honest, I am deeply suspicious of any nonfiction about Korean history or culture unless it was a translation of a Korean source. But one of the chief primary sources for Korean folklore and mythology is Samguk Yusa, which is available in English translation (Amazon). I highly recommend it!
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There are other titles that I haven't tried out myself but seen recommended, like Antique Gift Shop and Time and Again (the latter might be more Chinese than Korean though).
Hm...I don't really have any nonfiction recs precisely--to be honest, I am deeply suspicious of any nonfiction about Korean history or culture unless it was a translation of a Korean source. But one of the chief primary sources for Korean folklore and mythology is Samguk Yusa, which is available in English translation (Amazon). I highly recommend it!