Day 1

Unkown to our characters, we've been pulled into the Planscape game setting
Tux and Cas have been pulled through the rift and into Gehenna. We end up on the side of a steep mountain. Lava flows down towards us, and we quickly make the decision to move upward. Cas climbs the hillside and Tux uses Malik's immovable rods to climb. Before long a harpy comes up on us.
It speaks infernal, and is not understood by Tux or Cas. Luckily the harpy also speaks draconic. Cas takes command and tells it to "take us to your superior." Tux is uneasy with the plan.
"We need to get out of here" Cas insists. We find out that we're headed for a war camp that is part of the Blood War. Awesome. We send the harpy off, it doesn't know we can fly, and fly away as a harpy and a hunting bat. Heading for the mountains, we follow the river up to the top. It seems safest place in this hot and ashen plane. The call Gehenna the Bleak Eternity and The Fires of Perdition, which feels about right. Looking up, the river appears to be falling out of the sky. Nothing left to lose, we follow it up to it's source: a large earthen cone and out of this plane.
The top of the cone is a plane of rubble and desert. We don't know it, but this is Baator, the plane where our friends have been thrown to. Mountains spot the desert and a nexus of rivers that cross the surface of the desert. Many of the rivers go down into pits. Some of the rivers are blood.
We explore the surface from above. Many people-sized ants seem to be below us. Cas tries to speak common at the ants, they are part of a mining colony. In their conversation we learns that they are following THE RIVER STYX! It leads to Acheron. Whatever that is. Cas should have studied more in school, or she'd know more about how to navigate this wretched place. We fly on.
After a few hours of flying over the winding river, still in Baator, we are surprised to see Rick down below us. He waves at us in excitement. Rick lets loose that "someone" is looking for us. He cracks his whip. "They" might be able to see us now. Time to go, and quickly. We fly straight up for an hour, hunting for a way out. There is nothing but smoke and clouds. We get back down in easily 5 minutes. Not escaping that way.
We grab Rick and keep flying up river. After a few hours, we reach a point where the river flows straight up again. Flying creatures can be seen up ahead.
"Halt," one says as we near them.
Cas musters up her best commanding voice, "Good day to you soldier, carry on." They do not let us pass.
"We are under order to stop anyone from going this way and recruit them."
"You are under orders to stop and recruit commoners." Cas continues to push on, "that is not us."
"No, I'm pretty sure you're wrong."
Cas uses diplomacy to get past them, "how dare you question me??" she asks. They become intimidated and let us past. It's now clear that we're wanted, haste becomes even more necessary.
At the top, there is a mountain-sized crystal shard. Many crystals jut out out of its surface, this must be Acheron. An army wages on the plane: devils, ants and undead all fighting each other. We decide to follow the river, and avoid the battle as best we can. Into the mountains, a group of imps comes after us. Fighting seems imminent, but we fly away from them.
Tux finds us a cave to rest in. Our luck holds just enough to keep nighttime monsters at bay.
Day 2
We keep following the river up through the strange crystal plane, still unaware that we are in Acheron, the Eternal Battlefield. At the end of the river, it seems to be flowing out of the side of a large, black... thing, maybe a cliff side. There is a town just below the mouth of the river. We feel to have passed over another planar barrier. We decide to investigate in town. Tux will fly above the town while Cas and Rick go in and try to find a way out.A huge mountain looms over the town. Cas looks for a merchant's store, to find information. In the curiosities shop we meet Bill, a horrible creature made of many spider legs. He has no apparent body or face, but says hi and offers a leg in greeting. Cas shakes his "hand" and responds with an uncomfortable hello. She asks about the river. He doesn't know where it goes. She asks instead how to get "up." He asks if she means Sigil, but she doesn't know, but that might be what she is looking for. He tells her how to get through the gateway into Sigil. Cas buys three lead coins ("to keep the fairymen at bay") and a "key" to get through the gateway to Sigil. Knowing only that she wants to go up through the planes, they make for the gate.
Sigil turns out to be a large city, full of both demons and celestials and everything in between. We wander through the city, looking for a library or somewhere where we might find out more about why our own realm is breaking. The Hall of Records is near where we ended up. Walking in, a friendly lizard person is at the front desk, he makes us an appointment with Record Keeper Kevin for in three days.
