Unused Level 32

Super Mario 64 has 38 levels referred to within its level select, where seven are completely empty and go unused. Out of all of these, the 32nd level is the only level with any code assigned to it.

Unused Level 32 has code assigned to it that relates to the fish and cap switch objects, both of which have an unused value that checks for which course it is in. If it happens to be the 32nd course, then fishes will despawn if there is no water in its location, and that cap switches will start off unpressed bypassing its current state in the save file. The reason behind these conditions are unknown.

Theorising
It's assumed that Unused Level 32 belongs to a removed test map. The fact that the switches always appear as unpressed in the level could mean that it was intended to test the switch's behaviour when pressed, and the corresponding behaviour of switch blocks. A test level appears in Super Mario 64 DS and contains switch blocks, although they do not carry the same unpressed check as the original.

It's also possible that Unused Level 32 could be home to an unused course, most likely a cap switch course because of the checks for switches. It could belong to the mysterious Yellow Cap Switch.