The Temple of Dagon

Could someone give me a quick synopsis of this story? I read it already, I just think I might be missing some details that Lovecraft might have meant to imply(or maybe not).

I understand the noise of the rats drove him(de la Poer) and the others down to the cavern below the house. And then he was possessed by a demon or perhaps former ancestor and began to eat Norrys. It also mentioned something along the lines of this cavern being ante-hell.

So I'm just wondering, is this place really in fact the entrance to hell or it just "looks" like it could be such a thing? Also, is there anything else I'm missing? This story confused me quite a bit except for the outstanding details of him eating Norrys and the sounds of the rats in the walls. But besides the obvious things, I didn't really get any of the underlying things that Lovecraft meant to imply to readers.

Help?

I don't think it's Hell at all, just a large subterranean plaza once used as a place of worship to the Phrygian mother-goddess Cybele.

So was he possessed by a demon or an ancestor or what?

I think the guy had mental disorders passed down from relative to relative. It only needed a trigger to come out.

Sort of a "holy shit, this place is crazy..." followed by a flooding back of ancestral memories. I use a similar theme in "Dreams From Outer Spheres".