Ruins of Mezro, which you can buy right here.
You can watch this session right here:
(Shaun) Linnet - Human Druid
(Ashley) Lemuel - Human Rogue
(Jesse) Kyrin - Human Cleric
The heroes were in a large two story building that once held a market, trying to get a stone tablet that was situated in the middle of a zombie horde. It was lodged in the torso of a single zombie.
Theater of the Mind: I had a bit of difficulty describing this place. Half the zombies were on one side, and half were on the other. The first floor was full of lines of tables with products on them. The second floor held offices and desks.
Over-explaining: When you're in the moment, it's easy to either over-explain or under-explain the scene. If you overexplain, some players will tune out and then operate on their limited understanding of the scene. Players aren't keen on piping up and admitting that they don't understand the layout, I think they assumed they missed something.
To combat this, I will often reiterate the basics of the place as we play, to ensure I've communicated the essential details. As soon as I finish reading boxed text aloud, I repeat the bullet points to hammer home the things they need to know.
Under-explaining: If you under-explain, which I often do, each player has their own image of the location that is vastly different from what I had intended.
Accurate Descriptions: I think that when you're running a complicated location, you should probably have some kind of map to show them. Especially if you're running a major encounter!
Also, if a player does something based on misunderstanding the location (for instance, trying to jump a river of lava that they think is only 5 feet wide, not 50) you should rewind. If the mistake isn't realized until much later, you can probably let it go unless it had major consequences.
The Zombie Market: My idea here was that there are crossbeams above the horde. The group could climb on them, drop a rope, and pull up the zombie with the tablet lodged in it.
The group did not do that! They gathered on the second floor and smashed a hole through it, directly above the tablet zombie. They used their weasel, Iris, to draw the horde away. She was killed! She's a familiar, so she vanished and could be summoned again the next day.
I was very alarmed at this point. They were about to lower themselves into a room with 200 zombies!
The group lowered a rope through the hole and climbed down. Lemuel, the rogue, made a beeline for a potion stall that still had some potions intact. There was a zombie hidden under a stall that dragged him under. Linnet ran over to help.
Meanwhile, Kyrin was trying to pull the tablet free of the zombie. Its arms were tied, so it struggled to bite at them. Kyrin kept trying to make strength checks, but the tablet wouldn't budge.
Swarmed: The horde closed in on Kyrin and he was surrounded by about 20 zombies! The dude is 3rd level. I was worried that he would die. The group was able to get the attention of the horde and peel many of them off.
A batch of zombies started crawling under the stalls and tables to get at Lemuel and Linnet. The heroes ended up getting on the tables and jumping from one to the next, making their way toward a window that they could use to escape outside.
Kyrin finally got the tablet free as the zombies bit him a number of times. Then things got worse. Two zombies looked down at him through the hole in the ceiling. They were about to fall through!
He disengaged and fled.
While table-jumping, Linnet crashed through a rotted table and a crawling zombie attacked her. Lemuel got to the window, smashed it open, and called to their guide, Eku, for help.
Eku: Eku is one of the guides from the tomb of annihilation. She has a secret and is a mysterious, friendly old lady.
She came in and used her healing powers to keep the group alive as they made for the window. Thanks in part to Eku, the group escaped with the tablet.
They rested in the building where they'd defeated the goblins. They hated that zombie market and agreed that they were going to burn it to the ground.
The Tablet: They looked at the tablet and were able to figure out that it was a map. There are a bunch of magic obelisks in front of buildings in Mezro. If they are touched in a certain order, they just might open a portal to the real Mezro, which is hidden away in another plane.
Once rested, the group set fire to the market and began touching the pillars in order.
When they got to the library, they sent in to check it out. Zombies were in there, some browsing and some putting books on shelves. My thinking as that a long as the group followed the rules of the library (be quiet, get your books checked out before leaving) the zombies would leave them alone.
The group was amused by this and followed the rules. They found a bunch of books that give them information on the hag Nanny Pu'pu, who Eku had told them about, and the Sewn Sisters, a hag coven. They also read about Ras Nsi and the barae (protectors of Mezro with magic powers).
I had googled the barae, who are mentioned in older D&D products and novels. I described each of them to the group. There are tatues of the barae in the main encounter area of Mezro, so I wanted to set up what could be a very fateful moment in the temple.
That's where we stopped. In the next session, we added a fourth player and the group got hammered with wild magic.