If all mythology is true, you are looking at thousands of myth systems, so you may want to tackle them individually online, or at least the ones you want to tackle. There isn't really a comprehensive reference that large, at least outside an educational research setting, and even then I don't know of one. But Google may help on a pantheon by... See more

I think right now my favorite area is religious archaeology. Written records are possibly the largest source we have for dead religions, and in some cases, like classical Greece, we have loads of records of stories. However, in the majority of mainland Europe, we have middling to no pre-Christian accounts. Archaeology does its best to fill in the... See more

A more important factor when learning about myths is learning how to interpret them. There are a number of different schools/approaches here, and Campbell’s is one that runs into the problem of conflating similarities between cultures rather than paying attention to important cultural distinctions.