There is one pattern buffer in the starting room of the level. A hidden 3x shield recharger can be found in a corridor just to the north of the player's starting position. There is also a 3x shield recharger in a secret room overlooking a lake of lava. Finally, in the northern part of the level, there is a 2x shield recharger at the end of a lava-filled tunnel; using this recharger involves taking some unavoidable fire damage.
Use the pattern buffer next to you at the start of the level. Behind the door to the right of the pattern buffer you'll find an ammo cache (marked A on the map).
Go southwest through the corridor until you see a Juggernaut flying in a large lava-filled room. As soon as you see it, you should trigger some enemies. At this point, move back to the starting room and deal with the enemies that chased you (don't worry, the Juggernaut won't follow you back here).
In the starting room, interact with the wall panel with blue/white stripes in the northeast wall. It's actually a hidden door. If you woke up the enemies in the south room as described earlier, a 3x shield recharger is revealed here.
Now that you have a safe base of operations, with a pattern buffer and shield recharger you can return to whenever you need, you can set out and explore the level. This level is large and there are multiple routes you can take. You have to visit all parts and kill all enemies.
The Juggernauts are difficult to kill. There are plenty of rockets to be found in this level, so unload your rocket launcher on them. They also have a weakness for energy weapons, so if you're out of rockets use your fusion pistol or an alien weapon.
The way forward in the lava-filled room to the northwest of the starting room may not be immediately obvious. You need to jump across the lava down into a low-lying corridor at point B on the map.
After killing all enemies on the map, proceed to the northwest corner of the level. There will be a corridor there with several teleporters leading to different parts of the level. You'll find the exit terminal at the end of the corridor.
There are several secrets to be found in this level (any enemies encountered in secret areas don't have to be eliminated to complete the mission objective).
The lava river with two Juggernauts hovering over it in the middle of the level contains a ledge you can reach via rocket jumping (a Juggernaut's rockets will work, too). This is at map location D. You'll find a Hunter here, as well as an invisibility powerup and a secret Bungie Easter egg terminal.
You can grenade jump onto the platform in the middle of room E on the map. This will teleport you to a secret room (location C) that contains an invincibility powerup. The west wall contains a 3x shield recharger hidden behind a panel. The east wall can be opened to reveal a lake of lava; there is a corridor at the south end you can jump to to get back to the rest of the level.
The north room with the Juggernaut in it contains an invisibility powerup at location F, behind a wall on the west end of the center platform.
This Easter egg terminal is an "out-of-character" message from Bungie, detailing several things to try if you never figured them out.
This terminal contains another message from Leela. If all the enemies on the level are defeated, she apologizes for her earlier ramblings. She then tells you that Durandal has left the UESC Marathon, and says that she is terrified by the implications of his motives for assisting you against the Pfhor. She then tells you that there is one last place to defeat the Pfhor, and teleports you there to Ingue Ferroque.
- The music for this level is a song titled Landing. It was previously heard on Arrival and G4 Sunbathing. It is track #7.
- The named regions on the level map include "Engineering Storage" and "Fusion Vent #9". The latter name could imply that at least some of the lava encountered aboard the Marathon is actually superheated or radioactive waste material from fusion reactors.
Marathon - Level 25: Try again