Tower

The Tower (or previously The Spire) 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.

Plot
According to Prophetbot, the World is dying due to the loss of its sun, and Niko must return it to its place in the top of the Tower. Along their journey, Niko draws closer to the Tower, and its entrance room can finally be entered through the Refuge.

Original
After completing the maze The Entity put Niko through, they arrive at the location started. They go to sleep at the bed and find themselves in a dark area with an elevator door. The elevator takes them to the summit of the Tower, where the Player must decide whether to return the Sun or save Niko.

Remake
After obtaining the three items with yellow phosphor, the Tower can be entered by standing on the X in the entrance room and closing the game.

Upon entering the Tower, Niko finds themselves in a blank abyss. They do not have the Sun and are unable to contact the Player, which makes them increasingly upset. After some wandering, Niko finds the computer. The Entity congratulates them on returning the Sun and tells them that when they go to sleep, they will wake up at home. Niko is reluctant to listen, but goes in the bed by the computer anyways. The Entity tells the player to leave and not come back, then closes the window. Relaunching the game shows Niko in a bed. Pressing any button will close it.

At this point, The Author changes the Player's background with a message to open a file in Documents/My Games/Oneshot. Doing so and reopening the game will show you a dream sequence before Niko wakes back up. The Entity becomes furious at the Player for returning and traps Niko in a seemingly endless maze. The Player has to use the file they opened to navigate it. The Author communicates with the Player throughout this. He tells them that Niko must shatter the Sun to go home and returning it would trap them there forever.

After completing the maze, Niko ends up on a catwalk in the shape of the Sun, in the middle of which is the actual Sun. Before Niko picks up the Sun, they are somehow able to communicate with the Player again. Picking it up transports them to where they first found it. They leave through the door they came to the Barrens through, but it leads to a hallway this time. The Entity will contact the Player again here, asking them to break the Sun to send Niko home.

At the end of the hallway is an elevator. During the ride, the Player has to tell Niko that the only way to go home is shattering the Sun, as in this version Niko is not told. After the long ride is over, Niko steps out into the summit. There, the Player decides whether to shatter the Sun or go home.

Trivia
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 * According to Silver, the Tower has existed "from the beginning of time." Whether this refers to the Tower in the Old World or simply the World is ambiguous, though it could very well be both.
 * The Tower is a very cryptic structure, with seemingly impossible room structures and loops that require outside help to overcome. However, this may be due to the World Machine's influence.
 * The Tower's power is strongest at the summit, where the Sun is placed.
 * According to a child in the Glen (and thus more according to their grandfather), the Tower is constantly spinning in order to light up all of the World, similar to the motion of a lighthouse.