One of the Star Fox 64's best features is its alternate missions paths. Here's how to access them.

Aquas:
Score 100 kills or higher in Sector Y to warp to Aquas, the submarine level.

Area 6:
When you hit the last leg of the Macbeth stage, shoot the red pillars with metal direction flags on them so they turn green. Keep a very careful eye out for them. (Hint: If you went to Zoness before Macbeth, Katt will come and help shoot those hard-to-reach switches.)

At the end, where the switchboard light is, a switch will appear. Quickly shoot it and the track will move to the right and watch the boss crash into the supply depot. After a nice 50-point bonus you're off to Area 6!

Sector Y:
When Falco is in trouble in the first level (Corneria), shoot at the planes that are following him to save him... He should say, "I guess I should be thankful". Later, when you come to the lake with the seven stone arches, fly through all of them. After the third or fourth arch, he should say, "Pretty smooth flying, Fox". After you go through the seventh arch, he should lead you to another boss. Defeat him and advance to Sector "Y".

Sector Z:
In Sector X, keep left at all times. You will eventually hit an area where you have to quickly destroy white gates to pass through them. Destroy the gates and pass through all of them to warp.

Solar:
When Bill tells you to destroy the 4 hatches, destroy them and then destroy the enemy core.

Katina:
Near the end of Meteo you will see rings made of sharp triangles pointing inward. Go through one and you'll jet forward in a barrel roll. Go through all of them (very tough) and it will make you fast enough to warp to Katina.