Long ago I experimented with that on Unity. Making the model on Blender was a learning experience.
I made the landscape with procedural generation. The heightmap was a texture looping on one axis, and modifiers allowed me to add buildings while the landscape was on a flat plane before I toggled and could see the result as a cylinder.
In-game you could walk/fly around the thing.
Sadly I was too busy to avoid homelessness for the next two years to continue and never got the momentum back