Castlevania 64/Duel Tower and Tower of Science

Conveyor belts area
After the lift and before the first door, there is the first white save crystal.

Machine guns room
Science Key 1 is after the first door in the big square room.

Navigate around three sides of the square room, and enter the door on the same side where you came in. Use the Science Key 1 to get the Science Key 2.

With the second key, go back to the large room and cross the chasm to get back to the start. Use the Science Key 2 on the door in the corner opposite the one you enter the big square room.

Behind the corner in the next small room is the second white save crystal.

Top room
Secret: Right past the door, there is an invisible ledge that leads to the isolated platform. Break the crate for lots of goods.

Use the spiked boxes to shield from the machine guns. After three series of machine guns and conveyour belts, there is the third white save crystal.

Optional: in the next small room you can find the Science Key 3. If you backtrack to the beginning of the large room, you can unlock the door to a room with a few items.