Roguelike Dungeons

Roguelike Dungeons is a mod by Greymerk that adds sprawling multi-tier dungeon "towers" to your world. Containing custom mob spawners, chests containing loot and various themed rooms. Creeper spawners and Enderman spawners are just a few different dungeons to note with rooms to themselves which also makes it a great place to create a grinder or to harvest spawners if you have another mod with that capability.

It is a standalone mod and is compatible with most mods:

Towers
This is what you're looking for if you want to attempt to take on a roguelike dungeon. They're found scattered around the world but I mainly find them in the flatter biomes (I need certification on this but I've never found one in a mountainous biome!)

They consist of the outer tower which contains a chest in the top room and is also a good place to set up a base while you raid the dungeon below. As you go down the first spiral staircase from the top room the next floor has 4 doors which are usually at ground level and is probably the main way you'd enter and exit the tower. As you carry on going down you'll arrive in a room with 3 archways blocked with iron bars, this is where the fun begins. As you break down these bars and travel into the dungeon you'll face the custom spawners and custom rooms, you aim is to raid as much loot as you can and keep an eye out for the next spiral staircase down. There is 5 floors in total with the loot getting steadily better and the monsters steadily harder the further you progress down.