Samhain is a town built next to the gate between the Unseelie Court and the world of the dead.
It is difficult to say for certain where in the multiverse Samhain lies. Some say it is in Pandemonium between the realm of the Unseelie Court and Tuonela, the afterlife of the Finns, though tales whispered by escaped souls claim the labyrinthine tunnels beyond the Death Gate lead to every land of the dead that ever was.
Once a year, on October 31 (or the local equivalent), the gate opens. The Dark Faeries come in. The souls of the dead come in. And a third gate opens to the mortal world, and on this one night the dark faeries and the unquiet dead can mingle among the living and no god or power can stop them.
The rest of the year, Samhain is a purgatory of sorts in which those faeries who for whatever reason find no welcome among their kin in the Unseelie Court live among those unquiet souls who have managed to temporarily escape the wardens of the dead. There are also a few mortal witches and shamans strong enough to live in Samhain without being stolen away by one faction or the other.
No one knows who created the gates. They look like crude archways made of massive stones. The locals call the builders the Old Ones and believe when they set the gates in place they also set in place laws that no spirit, faerie, or god can disobey.
The Mortal Gate leads to countless mortal worlds. The Death Gate leads to countless realms of the dead. And the Unseelie Gate leads to countless dark faerie realms, from Svartalfheim to the Unseelie Court to the wicked realms of the fomorian kings to the realm of Cegilune, queen of the hags to the Court of the Shadow Fey.
Besides the Death Gate and the Mortal Gate and the Unseelie Gate there is a fourth gate that leads up a narrow, winding path carved into the roots of the World Ash Yggdrasil. At the end of the path is Yule, a small town in Vanaheim inhabited by liosalfar, the Light Elves whose race mostly inhabit the neighboring realm of Alfheim. The light elves are all Ringivers, generous to a fault to lost travelers, but they are fierce warriors keen to defend themselves from dark elves who may try to ambush them through the Yule Gate in Samhain and keen to raid Samhain to avenge any slights they may feel they are owed. Some say they serve the spirit of Winter or the North Wind, while others say they serve Odin or his son Baldur. A gate in their own town opens to the mortal world on December 24, when their master rides out on unguessable missions. In Samhain, some have speculate that he pays tribute to Hell on that day, meeting with agents of the archdevils on a crossroads to gift them with treasures created by the light elves during the year.
Mostly the light elves are too fierce for the people of Samhain to use that gate. The gate has sealed off from the Samhain side in recent centuries and avoided for the most part except on one rare occasion. When a god dies and returns to life, first his shade passes through the Death Gate to Samhain, and must reside in the town with massively reduced power until the gate to Vanaheim opens up. Only then he walk the narrow path up the World Ash and emerge in the light, covered in power and glory.
The mayor of Samhain is Jack, a tall, skeletal figure in a fine white suit. Some say he was a former consort of the Queen of Air and Darkness who got on the queen's bad side. Others say he's a son of the god of the dead and the goddess of autumn, disinherited by both of his parents. He rules uneasily, striving to keep a balance between the ghouls, boggarts, witches, ghosts, goblins, necromancers, dark elves, and scarecrows who make up the town's population.
Ahh, a place for all the long-leggedy beasties and things that go bump in the night. A good idea. They're probably a little underrepresented in Planescape. Nice use of the Ringgivers, too. I suppose Valentines Day Town (or Easter Town, now) would be next, but honestly I'd be more curious about Thanksgiving Town.
Much appreciated.