Temple of the Underworld: Adventures on the Planes

I have been playing a new campaign for a few months now. It is 5th edition Dungeons and Dragons rules in a campaign world of my design. It is focused on a megadungeon called the Temple of the Underworld, which was, as it's name suggests was devoted to deities of the dead or the underworld. The elven deity Labelas Enoreth, though devoted to longevity, is the closest thing that the elves have to a deity of the dead and thus also worshiped there.

The first couple of sessions were rather routine explorations of the first level of the dungeon, with a very brief foray into a flooded sub-level. However the campaign would be uprooted by the actions of the dwarven fighter Grell defiled a shrine devoted to a demigod son of Zeus. This angered Zeus, so Zeus sent a spirit to confront the PCs and give them a quest to fulfill. They were to travel to the Temple of Zeus far to the south and present themselves to the priest their for further instructions. They... didn't make it.

In order to get horses to expedite their journey they agreed to do a task for the local count. They followed a map to what was once a bandit's lair, but turned out to currently be inhabited by orcs. They did alright at first, but due to my lack of understanding of 5e encounter difficulties ended up running into an overwhelming group of orcs that quickly defeated them (I am strongly considering using converted stats from 1e or 2e rather than the existing 5e stats). Instead of allowing this to end in a TPK I judged that Zeus, wanting to insure that the PCs did not die without fulfilling their obligation to him rescued them.

They awoke in the presence of Zeus himself. Zeus bade them again to go to his temple, but this time the one in the extraplanar city of Sigil. The PCs agreed, but before leaving Olympus sought an audience with Ares, who granted it because the Count was preparing for a war and had his favor. So Ares granted them another quest in exchange for assistance, including a guide, which was a new PC (one who only showed up for one game as it turned out). The PCs then sought out the Great Eagles of Zeus, the descendants of the giant, golden eagle that is Zeus's personal companion.

Before they made it to the roost of the Eagles they encountered a dryad in a grove on the slopes of Mount Olympus. It charmed their guide and when they attempted to leave with him she summoned two wolves to attack the PCs. However they were able to smooth things over by mentioning their obligation to Zeus. When they met the Great Eagles they again mentioned their obligation to Zeus in order to secure their aid. Thus they secured a ride to the town of Thrassos, where there was a portal to the gate town of Glorium, from where they could get to Sigil. However, to access the portal they needed the consent of the town elders. It took some time to secure that consent from the busy elders, so while they waited they sought out a mage to send a message to the Count on the Material Plane. The halfling rogue, Himaru, was dismayed that unlike many of his companions he could not see in the dark and so commissioned a magic item that would make up for this weakness. The mage agreed in exchange for money, trade and a service. It seemed a certain house in town was the site of mysterious events.

They set out for the house and quickly experienced a number of strange phenomena, including two parallel passages that led back to the other and an unusual creature, like an ambulatory bush that was responsible for the strange phenomena. I used the The Random Esoteric Creature Generator by James Raggi to create this creature. They did not want to fight this bizarre creature and so parlayed. The creature seemed interested only in being left alone, so they left, but warned the creature that they could not guarantee others would not come. They did advise the mage of what they found. The PCs also took on another quest in order to hopefully expedite their audience with the elders. They pursued a priest of Loki to a nearby cave where they discovered a hidden, ruined temple to Loki. They soon found the priest, accompanied by hirelings and learned that he was searching for what he described as a Hammer of Thunderbolts with a short handle.

After a short time they fought a group of norkers and their orc allies. While the PCs were dealing with a group of goblins that arrived as a random encounter, pursuing them as they fled, the priest and his party slipped away and discovered their goal in a nearby hidden room. The PCs soon realized what was happening and hurried after them, discovering the priest trying to tip over a pedestal so that the hammer would fall in. After the battle the PCs realized what the hammer was, no mere Hammer of Thunderbolts but the Hammer of Thor himself, Mjolnir. The PCs resolved to return the hammer to Thor, not wanting to anger him by trying to keep it, not that they had any way to use the hammer. Of course by hindering Loki's priest they attracted the attention of Loki, but would hopefully have the favor of Thor.

After another week they elders could finally let them through the portal. In Glorium they sought out the Temple of Odin, which contained shrines to other deities, including Thor. They prayed at the shrine and Thor himself appeared. After a demonstration in which a tree was demolished by Mjolnir's power Thor granted boons- Boots and a Cloak of Elvenkind for the rogue and a ring of Enlarge/Reduce for the dwarf. Thor also directed them to the portal.

Finally they arrived in Sigil, the portal leading to the Great Gymnasium, headquarters of the Transcendent Order, one of several factions that held influence over the city. They were ushered out of the building by guards as the gymnasium was closed to the public at that time. They sought out a guide and found one, an Azer. He agreed to show them to the Temples of Zeus and Ares in the city and they got their new quests- find the relic that started the whole thing and bring it back to the Temple of Zeus and travel to a dungeon on the world of Abeir-Toril and share it with the Count. They were able to find a portal that led to the depths of the Temple of the Underworld (one I intended for them to find during there adventuring originally) and started searching for the shrine, since they came out in an unfamiliar area. They encountered Manes demons and Shadow Demon and a swarm of ambulatory fungi, before deciding to take a rest, which is where things stand now.