Cavern[edit]
You may find the third cavern a bit more challenging than the earlier ones, primarily due to the degree of difficulty of getting through to the fortress entrance. There are a number of times where you are presented with a very tall, insurmountable pillar, and you must jump very high in order to shoot out a section that you can jump through. As long as you remember to hold down while jumping, you will be able to jump high enough to hit those blocks. You may notice a strange type of force field that floats at a specific height off the floor. You must avoid touching this field as it drains Layla's health. Additionally, the game ups the challenge by making your work twice as hard for life restoring food. Food will now only appear from every other enemy that you kill. The entrance to the secret room is on the floor, but you'll have to shoot out a couple of blocks that lie between the floor and some falling spikes in order to reach the elevator. You will see a B and a II on the wall, indicating that the password disk is found on the second basement.
Fortress[edit]
The third fortress is far more complex than the previous two. However, if you study the map, you will come to realize that if you follow the correct path to the password disk, you will actually pass through it in roughly the same time that it took you to complete the first two fortresses. From the fortress entrance, make sure you drop down to floor B1, and cross through that hallway in order to find another gun upgrade. Then take the elevator down to collect the password disk. When you leave from the password area, you will warp all the way to one hallway away from the boss, bypassing a huge extent of the fortress.
Around the fortress, you will find a large quantity of a particular enemy. This enemy bounces up and down between the floor and ceiling quite fast. It is difficult to destroy (however two bazooka shots can destroy it) and it reflects your bullets back at you, although very slowly. It is best to ignore these enemies entirely and continue running through the hallway. Defeat much weaker enemies to collect food and restore any health that you lose running through the tougher ones.
Boss[edit]
Unfortunately, past experience will mislead you in the fight against the third fortress boss. Not only will it take much more than a single Ax throw to kill this boss, Axes won't even harm this boss at all. Fortunately, there's a very simple technique to defeating this boss. You'll probably want to rely on the machine gun. The boss snakes throughout the room, following you from one side of the room to the other. He tends to get low to the ground in order to hit you. Once he is low to the ground, stand in a corner and fire your machine gun at him. When he gets too close, leap over him and stand in the opposite corner, and resume firing at him. Continue doing this, and the boss will go down fairly quickly. Not only that, but you'll get bonus food from every segment of its body.