This adventure is designed for 4 characters playing at 1st level.
For centuries the Vault of Balla was considered lost. A hunter trying to escape a terrible thunderstorm recently rediscovered the vault as well as a terrifying giant spider that has made its home there. Deciding the spider was too much of a threat, the hunter headed back out into the storm and eventually made it back to the village.
A highly valued species of fungi called Sippler's Shroom was discovered growing in the vault, so the locals want the Vault cleared out in order to create a means of income for their village. They are offering 200 gp total as a reward.
Sippler's Shroom: This slender mushroom grows in clusters. It has a white cap and the stem glows a flourescent green. If eaten raw it is poisonous, but can be made into a beneficial tea when boiled. When ingested, the tea grants the drinker 2 hours of poison resistance.
In order to determine the amount of fungi in a room roll 1d4.
1 = There is no fungi in the room
2 = There is a little fungi in a corner of the room
3 = There is a large patch of fungi growing on the wall/ceiling/floor
4 = Every available surface in this room is covered with fungi
The entrance to the vault is thick with cobwebs. Everything is dusty and other than the footprints that were obviously left by the hunter, this place looks to have been abandoned for a very long time. To the north is an archway leading into another room. To the south is a huge double door with two keyholes.
This room is quite large and contains large statues of various gods trimmed in gold. On the west side of the room, a skeleton is slumped over on the floor and there are several crossbow bolts mixed in with the bones. A large fresco on the ceiling animates when looked and 3 Swarms of Spiders leave the fresco and attack.
2a. Door to Room 3: Closed / Unlocked / Trapped --> Trigger: Opening the Door / Effect: Crossbow bolts shoot out from the North wall to the South wall. Any character standing within the specified area takes damage. Damage: 1d4 bludgeoning. / Area: 15 ft wide / Detection: Perception Check (DC 15) / Investigation Check (DC 10) / Special: Effects of the trap are not visible to anyone who is unharmed. / Disarm: Thieves Tools (DC 10) / Intelligence Check (DC 15)
2b. Door to Room 4: Closed / Unlocked / No Trap
2c. Swarm of Spiders
On the far side of this room there is a very large crack in the wall that goes from floor to ceiling. Inside of that crack is a key. There is absolutely nothing else in this room.
3a. Find the Key: Perception Check (DC 15) / Investigation Check (DC 10)
This room contains an extremely life-like sculpture of an elf druid. The sculpture is holding a key in its fist very tightly, almost like the key is a part of the sculpture (it isn't).
4a. Get the Key: If the players speak to the sculpture in Elvish it will animate and if they ask it for the key it will give it to them. They can also try to break the key from the sculptures hand with a Strength Check (DC 15).
The door to this room can only be opened with the two keys found in other parts of the vault. It is a large room with a beautiful giant fountain in the center. There is no water in the fountain and if it is approached 3 spiders will climb out of it and attack.
5a. Door to Room 7: Closed / Unlocked / Trapped ---> Trigger: Opening the Door / Effect: Localized Earthquake. Attack roll determines if a player takes damage. Damage: 1d6 bludgeoning per character. / Area: Entire Room Detection: Perception Check (DC 15) / Investigation Check (DC 10) / Special: Large rocks will fall from the ceiling and then disappear. / Disarm: Thieves Tools (DC 10) / Intelligence Check (DC 15)
5b. Door to Room 6: Closed / Unlocked / No Traps
5c. Spider Stats
Boss Room. There is a large alter area at one end of this room. Resting on it are two giant spiders. Behind them is a very large chest. If done quietly enough, the giant spiders will not see the players at first.
6a. Giant Spider Stats
6b. Large Chest - Choose from any of these items, choose all of them, or choose your won. ---> 3900cp, 2000sp, 160gp (399gp) / Black Velvet Mask stitched with Silver Thread (25gp) / Cloth-of-gold vestments (25gp) / Copper chalice with silver filigree (25gp) / Gold locket with painted portrait inside (25gp) / Pair of engraved bone dice (25gp) / Silver ewer (25gp) / Blue quartz (transparent pale blue, 10gp) / Blue quartz (transparent pale blue, 10gp) / Eye agate (translucent circles of white, 10gp) / Malachite (opaque striated light and dark green, 10gp) / Moss agate (translucent yellow-white with mossy green markings, 10gp) / Turquoise (opaque light blue-green, 10gp) / Treasure total: 210gp
6bb. Adamantine armor (scale mail) (uncommon armor) / Boots of elvenkind (uncommon wondrous item) / Zone of truth Spell Scroll (uncommon scroll) / Wand of Conducting (common wand)
This room contains a small chest with 4 Potions of Healing. There is nothing else in this room.
Resources
https://watabou.itch.io/one-page-dungeon
https://tetra-cube.com/dnd/dnd-statblock.html