Rusty Bucket Bay (Banjo-Kazooie)

Rusty Bucket Bay is the eighth world of Banjo-Kazooie, many fans considered this world as the hardest and most frustrating one in the game.

Why It's Rusty

Rusty Bucket Bay is a massive difficulty spike, considering that Banjo-Kazooie is made for kids, that says a lot.
The oily water is poisoned by Grunty so that you lose oxygen twice as fast when in the water and you also lose oxygen when on top of the water. Many Jiggies require diving underwater and will likely get you killed.
The infamous Engine Room section inside the boat contains two Jigsaw Pieces. The one that's trapped between the propellers requires you to activate two switches in the boat to slow down the rotating blades blocking access to the Jiggy enough to not be killed instantly. However you only have a limited time of 65 seconds to reach the Jiggy before the fan is restored to normal speed. What makes it more frustrating is that the platforms rotate as well and are very likely to knock you into the bottomless pit.
Rusty Bucket Bay is the first and only level in Banjo-Kazooie to have bottomless pits, INSIDE A FREAKING BOAT of all things (It takes the form of a pit of boiling oil).
In the Nintendo 64 version, dying causes you to lose all your notes, meaning you'll have to go back to the Engine Room every time you die because there are notes there.
There are lots of rooms hidden behind breakable windows but those windows don't have any visual cues to let you know they are breakable. First time players are very unlikely to ever figure out those rooms exist aside form pure coincidence.