In ancient Egypt, soul houses and false doors connected the living and the dead
atlasobscura.com
atlasobscura.com
Saul from the book of Samuel tried to talk to a dead Samuel, and was divinely bollocked for it. (https://www.biblegateway.com/passage/?search=1+Samuel+28%3A1... or more fun, rendered in lego: https://thebrickbible.com/legacy/david_vs_saul/saul_and_the_...)
the Sumerians also had local accommodation for their dead, with libation tubes to provide sustenance for them in the after life. Irvine Finkel in "first ghost" explains this really well, and entertainingly. Do get the audio book if you can.
By the way, if this kind of techno-occult crossover thing is your jam, read the Laundry Files.
— Gandalf
The afterlife and dreamland are one and the same?
You see it in other cultures too. Little houses for the spirits and little people. In japan, Scandinavia...
It also reminds me of the demon in "The Exorcist". A master of language and also bound by it. A creature of theater.
To move from one world to another.
To enter a movie, story, game... we are all pretty familiar with that.
Output... maybe watch for phenomena in your imagination (which becomes distinctly visible in half-sleep, hypnagogic states, certain kinds of meditation, drug induced hallucinations)
If you are good at visualizing you might be able to use that instead of carpenting up an elf house. You might end up with a technique similar to that used by the Pure Land Buddhists.
Things escalated from there...