Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download 53 Low-poly Skyscrapers (Day & Night) Free.
53 Low-poly Skyscrapers daynight v2.0
53 unique low-poly skyscrapers. They are easy to use, as in the background.
The total number of polygons – 1300 and this is very important in the construction of large scenes like а city. These models use 10 materials with 20 textures 512×1024 resolution. On the 2 Channel created light maps. Skyscrapers will look very good in your projects. The second version adds night textures of building. I hope this stuff will be useful for your projects! I’ll appreciate your feedback! Enjoy and good luck!