Cavern[edit]
The enemies of the sixth cavern are very similar to the enemies of the previous cavern. The tricky part of this stage is the layout. There are a number of features in this stage that require a little thought. Early on, you are presented with a pyramid of platforms, and every level contains the potential to get hurt. At first glance, it seems like the middle platform is your best bet, but if you get on the highest platform, you can knock out the blocks that get in your way with Axes, and pass through fairly unharmed. Later on, you will encounter a single crate on the outside of a walled in platform containing many crates. If you don't shoot the outside crate, you can use it to reach the walled in crates and the items they hold. Further on is a tricky section of blocks that you must shoot out, step on, and head butt in order to create a clear path forward. You will have to deal with some blocks to your left to complete the maze. There is also a section with a high pathway that is difficult to reach unless you get a running start, headed to the left, and up and over the lip of the platform. If you take this top route, you will be rewarded with a cache of crates, more than one of which contains a pistol power-up. Finally, the entrance to the secret room can be similarly accessed by removing the four gray stones that block your way forward, moving right just a little bit, and then getting a running start to the left, and up and over to four crates. Destroy the crates and stand in the position indicated by the snapshot. There is no secret message in the secret room.
Fortress[edit]
Compared to the previous fortress, this fortress is a breeze. You can be in and out of it in very little time. It is far more forgiving in that you can return to just about any section of the fortress at any time, so you don't need to do anything in a particular order.
From the start, continue taking the elevator all the way down, and you will arrive at the password disk room. Collect the disk and take the elevator out, which will deposit you on the third basement. Run to the end of the hallway, and up one flight, and run to the elevator at the end of the second basement. This elevator deposits you on the third floor. Without moving, take the elevator down. You'll want to drop down to either the second floor, or the first or second basement. The next elevator that you arrive at will take you to the fourth basement, with the second basement dropping you off closest to your destination.
In the fourth basement, you'll want to advance to the elevator marked with the red "d" on the bottom. This elevator will take you to the fourth floor where you can access the boss. The elevator to the boss arrives ahead of a little bit more of the floor to the right. You may be tempted to climb up and destroy the large collection of crates, but don't be lured into a trap; the stage ends with a gap in the floor, and even though falling through the gap puts you back on the fourth floor, you pay a huge penalty for falling. In the end, you will lose more from falling than you gain from the crates. Instead, advance directly to the boss.
Boss[edit]
The boss of the sixth fortress looks like a differently colored version of the very first boss. He behaves identically to the first boss, but he is much stronger. In addition to requiring more hits to defeat, he is completely invulnerable to Throwing Axes, so you'll have to rely on bullets or your flame thrower. The flame thrower makes an effective weapon, but the machine gun ensures a little more accuracy if you don't mind using up a lot of ammo. Since this boss likes to jump around a lot, it's actually not too hard to stay a small distance away from him and count on him jumping over you quite a bit, but use this plan carefully. It may just be safer to shoot him from the opposite sides of the room.