Unreal
I decided to grab some random free unreal assets to see what kind of level I could come up with. After downloading a few packs and getting them in the engine, I decided that I would go with the medieval dungeon theme. But the amount of assets in that pack were fairly small so I checked to see if any of the other assets packs I downloaded could work on top of the dungeon ones without clashing thematically or artistically.
I had blocked out the first section of the level on a paper map before deciding to use some cave themed assets with the dungeon assets. Then I put the assets in place for the first block of the level. The overview of the result is below, as well as a walk through of the level.
Another unreal project I did way back when was in school with the prompt of the player having to deal with some sort of monster. I decided to go with an alien sphere that fed off of organic life. It was mostly cut scenes with two areas where the player needed to avoid being "seen". an overview of the level along with a brief walk through is below.