Saros Guide: All Biomes in Carcosa

Saros has 8 distinct combat biomes spread across the moon of Carcosa, two more than Housemarque's previous game Returnal. Each zone has its own visual identity, a named boss called an Overlord, a fixed number of Halcyon collectibles (with one exception), and a stack of Audio Logs and Text Logs for lore hunters. Runs through individual biomes tend to be on the shorter side, but 100%-completing any single zone takes considerably longer than a clean clear.

What is the Passage and how does it work?

Before getting into the 8 proper biomes, there is the Passage. Technically not a combat zone, it functions as the central hub you return to after every run, whether you cleared the boss or died trying. A few things worth knowing about it:

• Echelon IV NPCs are stationed here and provide story context as you progress.
• The Banyan Tree above the hub connects to story segments required for the Epilogue and the true ending.
• Primary is the main console where you upgrade permanent Attributes, unlock skills, review Carcosan Modifiers, and fast travel to any biome you have already reached.

Think of the Passage as your base of operations between every run. Spending a few minutes here after each death or clear is worth it.

The Passage hub and Primary console

All biomes in Saros

Here is every biome at a glance, including boss names and collectible counts.

Yellow Shore is the only biome without a tracked Halcyon count. The resource drops from Alpha hostiles and appears in containers or on the ground, but there is no in-game counter for it.

Shattered Rise

Boss: Prophet | Halcyon: 8 | Audio Logs: 17 | Text Logs: 3

Shattered Rise is the opening biome, built around mountainous terrain and rocky corridors. This is where Saros introduces its core mechanics: starting weapons, the Artifact system, and most importantly, the Eclipse. The Eclipse shifts the state of the world, changing enemy behavior and gating certain areas behind its activation.

To reach the first Overlord, Prophet, you need to locate a locked gate and open it using a specific device found while exploring the interconnected valleys. Prophet is designed as a difficulty check on the game's fundamental dash-and-dodge rhythm, so do not rush it.

Shattered Rise also has the highest Audio Log count of any biome at 17, making it the richest zone for early lore.

Shattered Rise opening zone

Ancient Depths

Boss: Bastion | Halcyon: 12 | Audio Logs: 14 | Text Logs: 3

Unlock fast travel by defeating Prophet, and Ancient Depths opens up. This subterranean biome is built around tunnels and glowing caverns with rising platform mechanisms that reward vertical awareness. The key unlock here is Jump Network Pads, which let Arjun reach previously inaccessible ledges and hidden areas throughout the zone and in earlier biomes when revisited.

The boss arena is gated behind the Vault, a large central chamber. Getting the Vault door open requires clearing two side paths, and one of those paths is only reachable while the Eclipse is active. Plan your run timing around that.

Shattered Descent

Boss: Rhabdom | Halcyon: 12 | Audio Logs: 14 | Text Logs: 6

Once home to Echelon III personnel, Shattered Descent is a vertical, gap-heavy zone where falls can kill you outright. The Grapple system unlocks here, which is what makes the biome navigable at all. Swinging across chasms with the grapple transforms what would be a death trap into a movement puzzle.

This is the shortest biome in the game by a clear margin. Rhabdom is also the only boss in Saros with a single health bar, which makes the fight feel distinct from every other Overlord encounter. Do not mistake a single bar for an easy fight.

Shattered Descent also acts as a gateway biome, connecting to multiple other zones once you have the movement tools to reach them.

Blighted Marsh

Boss: Legion | Halcyon: 20 | Audio Logs: 10 | Text Logs: 1

The swamp biome. Blighted Marsh is packed with industrial pollution, proximity traps that explode if you linger, and poisoned waterways that erupt periodically to punish anyone standing still. The environmental hazard density here is higher than in the earlier zones.

Reaching Legion requires finding an elevator at the far end of the biome, but it is unpowered on arrival. You need to explore both branching paths and restore power to the terminals before the elevator activates. Rushing straight through without clearing the paths means hitting a dead end.

Acolyte's Haven is accessible through a hidden route within Blighted Marsh, so thorough exploration here pays off twice.

Blighted Marsh toxic environment

Desecrated Fortress

Boss: Architect | Halcyon: 25 | Audio Logs: 11 | Text Logs: 1

A once-grand citadel reduced to falling debris and shattered stonework after a large-scale internal conflict. Desecrated Fortress introduces Honorarium Sigils, which you collect throughout the biome and spend to access the Sealed Chamber.

The more significant unlock here is Eclipse Threads, an ability gained by exploring deeper into the fortress. Eclipse Threads lets Arjun traverse beams of light, which is how you reach the upper levels of the city and eventually the arena where Architect waits at the highest spire.

Acolyte's Haven

Boss: Shepherd | Halcyon: 35 | Audio Logs: 9 | Text Logs: 1

Accessible through Blighted Marsh, Acolyte's Haven is a dock-and-wharf biome built around floating platforms and combat-grapple navigation. The grapple points here only activate once Arjun shoots them, turning movement through the zone into an active puzzle rather than a passive traversal.

Shepherd is described across sources as one of the more cinematic boss fights in the game. The sequence requires activating a beacon at the edge of the docks first, then making your way to the Wharf for the actual confrontation. Do not skip the beacon step.

Cathedral

Boss: Priestess | Halcyon: 50 | Audio Logs: 13 | Text Logs: 5

The Cathedral has the highest Halcyon count in the game at 50, and it earns that density through genuinely unusual level design. The biome has its own internal gravity system. By activating specific mechanisms, Arjun can reverse his alignment and walk on the ceiling, which is where a significant portion of the hidden Halcyon nodes are located.

The boss arena is locked behind what the game presents as an endless staircase loop. Breaking out of it requires exploring two side paths and triggering a mechanism that drops a massive bell. Dropping the bell opens the path to Priestess and also reveals a secret optional area worth visiting for completionists.

With 13 Audio Logs and 5 Text Logs, Cathedral is also one of the denser zones for lore content.

Cathedral gravity reversal mechanic

Yellow Shore

Boss: King | Halcyon: Unknown | Audio Logs: 14 | Text Logs: 1

Yellow Shore is the third Act finale and the last biome in the game. Arjun's final permanent ability, Blazing Strike, unlocks here. Based on available information, Blazing Strike is a melee-dash move required to break the King's guard, making it mechanically tied to the boss fight itself.

The Halcyon situation in Yellow Shore is unique: there is no tracker, and the resource drops from Alpha hostiles, appears in containers, and can be found on the ground. The total count is unknown because the game does not track it the same way it does in earlier biomes.

With 14 Audio Logs, Yellow Shore ties Ancient Depths for the second-highest log count, so it is not a zone to rush through even if you are close to the ending.

How do you 100% each biome efficiently?

A few patterns hold across all biomes, based on information documented in the sources:

• Eclipse-gated content is easy to miss. Several Audio Logs and Text Logs only appear in rooms generated during the Eclipse state. If your Halcyon or log counts are short, check whether you have cleared Eclipse-only rooms.
• Look up constantly. Jump Network Pads and the Grapple system open high-altitude routes that contain collectibles invisible from ground level. Ceiling-walking in the Cathedral adds another layer to this.
• The Databank tracks your lore progress. If you are missing entries, the Databank in the menu provides hints about which biome holds the remaining pieces.

Despite individual runs being relatively short, fully clearing a biome takes multiple passes. The collectible density across all 8 zones means completionists will spend significantly more time in Carcosa than a straight story run requires.

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