Originally Posted by
John Venus
On the contrary, DC has even more secret worlds than Marvel does: Themyscira, Atlantis, Skartaris, Bana Migdall, Yara's tribe, the Hidden City, Gem World, Azarath and possibly even more.
For the Homo Magi:
JLA Vol 1 #160-164 introduced the concept. Though there are some dated elements to the explanation.
Books of Magic #1-4 is basically a magical tour of the DCU.
Secret Origins Vol 2 #27 shows the history of Magi from Dr Mist's perspective.
Justice League Dark Vol 2 by Tynion IV also explored the idea of magic and different classifications of magic users.
I'm sure there are more. Folks are free to suggest anything I've missed.