The lighthouse building is available later on in the game and is something that you may not have too much interest in at first. What does the lighthouse even do? It lights up the land for you. Seems kinda weird since this isn’t what a real lighthouse actually does. Either way the lighthouse is like a giant torch. When it is night time, it will bring light to a huge area of the map, allowing you to see everything in the area as if it were day time.
The first issue you will likely have with one of these is that you are unable to place the lighthouse. The game won’t let you build it as it will show up red on all of the areas of land you select. Since this is a bit of a special lighthouse, it needs to be build in a body of water. Like the off shore oil platform, you need to place the building in water.