Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download Modular Dungeon Kit Expansion 1: Stairs and MidWalls Free.
Modular Dungeon Kit Expansion 1: Stairs and MidWalls v1.0
REQUIRES MODULAR DUNGEON KIT – This is the first expansion to the Modular Dungeon Kit, allowing you to add multiple levels to your existing dungeons and stairs for getting to these new levels.
The Kit includes 8 variations of stairs, and the pieces used to make your upper and lower levels fit together. Also included are short corner pillars and a mid level wall, great for creating balconys or making sure your players don’t go flying off the edges of your dungeon. The final addition to this package is a simple hole in the ground that will fit seamlessly with the original dungeon floor taking up exactly 2 tiles.