"Where Do The Dead Go?"

Because Poul and Karen Anderson's The King Of Ys incorporates historical fantasy, Princess Dahut is able to know that her mother, Dahilis, has returned as a seal but she does not know where Dahilis' soul goes after it leaves the seal. The sea creature has communicated with the Princess but now has bidden her farewell.

Dahut asks her father the above question. He replies that there are many beliefs and that she, as a vestal, must know what the wisest Ysans think. But Dahut does not want to be told beliefs or philosophical thoughts. She has directly experienced communication with the seal. Not living inside a historical fantasy, what do we know on the subject? We have:

the primitive assumption that souls leave bodies temporarily in sleep and permanently at death;
multiple beliefs about where the souls go after that;
philosophical speculations and rationalizations at least from Plato;
allegedly revealed religions;
claims to communicate with the dead;
claims to remember previous lives or to experience postmortem mental states.

My observations are here and here.