Why does the door to spiral mountain in banjo kazooie nuts and bolts say "2" on it?

i was playing BK N&B and finally got 70 some jiggies, and noticed that the door to spiral mountain had a 2 on top of it.. that normally would mean that there was a level going before it, but i dont recall one... is there something i missed? or is it just a mistake.. it bothers me for some reason, and i cant let it go.. help