I have watched a few good YouTube videos on D&D planar and race lore recently, all on two channels mostly. There are others but I found these two channels really gave me a better understanding of many things relating to this server and as some of you might know, I have been kicking around Sigil quite some time.
https://www.youtube.com/channel/UC0GmsD ... VdAfpWaaKA
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https://www.youtube.com/playlist?list=P ... usM-6JjcI-