Tower

The Tower is a structure within the World that houses the Sun. It is located at the center of the World, surrounded by the Refuge. It is tall enough that it can be clearly seen even from a long distance away.

Details
According to Prophetbot, the World is dying due to the loss of its sun. Niko can try to save the World by placing the Sun at the top of the Tower. The Entity warned the Player though that their choices will affect Niko and they only have one shot.