Iron Fortress

Iron Fortress is a desert-themed level. It was modified from The Forbidden Tombs, and keeps a small section of the original level, close to the bottom left.

This is a Bonus Level, and as such has a large number of 10k blocks in the second half of the level, as well as numerous other prizes. However, it is not particularly easy to get that far and Iron Fortress should be treated like any other level, unlike Gardens of Ire. This is because Iron Fortress is also a Battle Level.

Left Fortress
This is a piece of cake if you arrived in the level with the Berserker helmet from Passage of the Ancients. Just break the rock block to the left, then push the steel block away to reveal the micromax helmet. Moving to the right and finding a way out of the fortress at that point is easy.

If you don't have berserker, grab just one of the helmets; you'll likely be needing the other later. Proceed along the given paths separately in order to break open the four barriers on the right side of this fortress:

Eyeclops
Reveal the shooter block to break the rock blocking your path to the left and go up. There are two rubber blocks to make this ascent easier. Immediately, there is a shooter block pointing right you need to reveal. Step on the ledge next to it to break a path open. There's another shooter block aiming downwards to open up another part, but be careful to not reveal the steel block below it; that will forfeit the level.

Once you've done this, simply reveal the two shooter blocks in the more open area to cause a chain reaction, breaking open two of the four barriers. Carefully move down the passageway to the right, which is quite tricky, to grab a nearby Juggernaut helmet, or simply return to the start if you haven't done the Juggernaut section yet.

Juggernaut
Move along the rows of steel blocks, then fall downwards. Move left through the pillars, and fall down to a series of areas blocked by a checkerboard pattern of rock blocks. Break your way through these to access a shooter block. This shooter block unlocks access to another shooter block in the lower left corner of the map, which breaks open one of four barriers. Another can be easily broken by moving up instead of left from the initial shooter block.

Rubber blocks allow you to return to the start from this position, but alternatively you can jump through a hole in the wall of this last room and navigating up a series of drill blocks.

Whichever route you take, you need to bring Juggernaut to the right-center area of the fortress once you've broken all four barriers.

Right Fortress
There are a number of ways to access an exit teleporter from here.

Juggernaut
If you explored the area around the first fortress somewhat, you should have found two shooter blocks. Activating them makes it easy to bring juggernaut right into the first teleporter. If you didn't do this, move slightly downwards and straight to the right, navigating through the shifting blocks. Be careful at the right-hand wall to break the prize blocks, then jump on top of the 2 rock block + 1 shifting block arrangement. This allows you to access the teleporter in the top right.

Micromax
If you move up immediately after entering, or jump in the right place while moving to the right with Juggernaut, you'll find a micromax helmet. Simply navigate the maze (it isn't difficult) in the upper section to reach one of two teleporters. There are also several prizes in this area.

Red Stealth
Above the archer leading into the fortress is a steel block. Jump onto it with Juggernaut, then jump to the left to reveal another steel block. Repeat until the Red Stealth helmet is revealed. Below the Juggernaut path is a set of rocks begging to be broken, so do so. This unlocks another area, which unlocks yet another area containing several prizes. It is easy to then navigate through the walls of rock blocks, then up the right-hand wall to the upper right teleporter.

Alternatively, you can use Red Stealth to break open the passageway to the first teleporter.

Secrets
This level has more, and more complicated secrets than just about any other level in the first two stages, other than perhaps Lost World 3.
 * There is a 10 diamond block immediately to the right of the start. It can be revealed with Eyeclops.
 * In the final room in the Juggernaut section for the first fortress, jumping between the two vertical pillars will uncover an extra life.
 * Above the right-center area of the first fortress, the amalgam of drill and rock blocks contains one extra life, at the bottom, disguised as a rock block.
 * After exiting the first fortress with juggernaut, moving immediately downwards and jumping correctly where the third barrier was originally reveals another extra life.
 * There is a hidden diamond between the two fortresses.
 * Bring Juggernaut across the Juggernaut path in the second fortress and reveal the Micromax and Eyeclops helmets. Grab the Eyeclops, and break the block containing Micromax without collecting it yet. Revealing the area to the left will show an assortment of rock blocks as well as a shooter block. Break all the rock blocks in the way, then reveal the shooter block, immediately collect the Micromax helmet, and activate the shooter block before it disappears out of sight again. Then break the second rock block further left with the other shooter block. Proceed to go back and collect the other Eyeclops helmet, which is hiding at the top of the nearby staircase of shifting blocks. Crawl through the lowest passageway; then, reveal a bridge of rock blocks to a secret area in the first fortress. There's also a 10k block along this path. The secret area contains a bridge to Elsewhere 8, an extra life, and a continue.
 * Grab Red Stealth outside the second fortress and break the rock blocks leading into the room with the archer. Then break the second set of rock blocks, but in a way that leaves a path back through. Then go left and jump onto the spikes on the far left of the room; crawl through them to exit the area. The next helmet to obtain is the Micromax above the entrance. Bring Micromax through the Red Stealth route, then to the right of the four prize blocks is a long, secret passageway that eventually leads nowhere. However, 60k points can be found in this area. Be careful not to get crushed Micromax can also be used to reveal a Berserker helmet on the left wall of the right-most set of spikes, which later unlocks a secret in Ruined Maze.
 * Instead of entering the second fortress normally, fall with Juggernaut onto a set of steel blocks, then jump through a hole in the wall.
 * The wall of rock blocks near the end of the Red Stealth path contains a disguised 10k block.

Trivia

 * The idea of bonus levels didn't exist in the mod until the micromax + six 10k blocks secret was designed. Battle levels have been an idea since the original map was made.
 * The odd puzzle revolving around switching between Micromax and Eyeclops is the second least-complicated bridge in the game, with the least complicated belonging to Forgotten Treachery.
 * When planning and creating the level, the first fortress was rigorously thought out, but the second one was improvised.
 * The area between the two fortresses is the most empty accessible space in any level.
 * The shifter block on the upper right area of the map can be pushed into the ghost blocks above it. If one does so, they will discover that the ghost block actually destroys the shifter block entirely. This behavior does not exist in any form for mushroom blocks.
 * The bizarre arrangement of shifter blocks below the Micromax maze are the remains of a failed experiment to create an elaborate secret involving mushroom blocks destroying assorted other blocks.
 * Playing this level requires one to skip Explorer's Cavern entirely, meaning the first cave level one would access on this route would be in Stage 2 or later. However, none of the cave levels in the game have to be played if one takes the right teleporters, meaning this level allows one to play 0 cave levels in the entire game if they choose. At least one Woods, Mountain, Marsh, Sky, City, and Hills must be played regardless of path. It is, however, possible to skip every Desert level; however, doing so requires you to play at least one cave level. It's also possible to skip every Island and Ice level (even at the same time), but that is far less interesting.
 * The slightly bizarre palette looks quite a bit different from the original due to some darker colors being made comparatively lighter than other, similar colors.
 * Other than Cave, Desert has undergone the most palette changes. It was originally a more red/orange version of the original Desert palette.

First Occurrences

 * This is the first Desert level.
 * Archers make their first appearance here.
 * The first bridge (other than the 100k trip) is here.