The Twilight Pyramid is an object from The Legend of Zelda: Twilight Princess. It is a nigh-indestructible, gold-tinted barrier made of a form of solid twilight that covers Hyrule Castle, preventing anyone from entering. If Link approaches the barrier on the bridge connecting the castle to Hyrule Castle Town, no weapons or items can be used, preventing Link from testing the Pyramid's strength up close except by rolling into it. From afar, Arrows and Bomb Arrows can be shot at it, but fall short. Barriers of a similar appearance and function enclose Link during fights within Hyrule Castle and during the final battles with Ganondorf.
Interestingly, a strange weather effect occurs in the vicinity of the castle, possibly caused by the barrier, which lasts throughout the game, even after the barrier is destroyed. No matter the time or how the weather is elsewhere, around the castle, as well as the arch and bridge in the northern part of town that leads to the castle grounds, it instantly becomes daytime and also instantly starts raining for as long as Link remains in the area. It should be noted, though, that this phenomenon begins only after Midna shatters the barrier; prior to that, the weather and time of day on the bridge will be the same as in other places.
Late in the game, Ganondorf creates the Twilight Pyramid in order to prevent Link from entering Hyrule Castle, where he now resides. However, when the reformed Fused Shadow has been recovered from Zant, Midna uses its power to transform into a mighty beast which destroys the barrier, gaining Link and Midna access to the castle grounds.