A bigger dungeon will only spawn in underground and it mostly found in y12 and y8 below, and has a spider spawner in center alongside the 4 chests protected by cobwebs, there is a small chance that will generate a map that leads you to the stronghold.
It is also called a reinforced tower that is almost impossible to go in, except the obsidian door that is the only way to enter. It contains 4 stories with 4 spawners inside, 1st floor has a zombie spawner, 2nd floor has a cave spider spawner, 3rd floor has a wither skeleton spawner, and the 4th floor has a blaze spawner, contain some good loot. Another thing that in first floor has a light gray wool near the entrance that if you break it, it will lead you to the secret sculk room underneath the tower, and has a large chest with some loot and a map that will lead you to the ancient city, but be careful out there because there is an active sculk shrieker inside meaning it can summon the warden, so, be cautious.
Spawn only in Plains, Taiga, Forest, Savanna and Jungle. It has a secret chest loot in one of the tombs, and has a small chance that will generate diamonds and enchanted books.
The link is mediafire, which is you can download it easily.
Must turn on these experimental features shown in the picture below before play or else the structures won't generate.
Warning: Do not reupload this to other sites without the permission of the creator. If you want to showcase this add-on on YouTube, I will allow it if you credit me.