This is a paid asset, but now you can download Forbidden Dungeons for FREE, Please keep in mind this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
For more detail this asset from the Unity Asset Store: Click Here
Forbidden Dungeons v1.1
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[Forbidden Dungeons]
With this pack you get the tools needed to create a dungeon environment. It can be customizable to create your own underground level. You can also mix the pieces with other environment tools. Included many lods in heavy models to improve performance. Inside this asset: 206 prefabs with different blocks to build scenes, decoration props, fxs, shaders, materials, high quality textures, etc.
Right now it includes 2 main zones (big room & sewers) wich also includes corridors, extra rooms and 2 different sewer style (small & big). This underground pack is constantly growing with every update including new different zones & assets.