Abyssus Keys Guide: Locations and Uses

Abyssus Keys Guide: Every Key Location, Door, and Reward

There are 12 Abyssus Keys in the game, and 9 of them unlock something that matters — the other 3 open shortcuts or cosmetic rooms you can safely skip on a first run. Three keys sit behind one-time story gates and become permanently unavailable once you cross the point of no return in the Drowned Cathedral, so the order you collect them in decides whether you finish at 12/12 or get locked out at 9/12.

This guide maps every key by region, tells you exactly what it opens, flags the three genuinely missable ones, and gives two efficient routes — one for a completionist run, one for players who only want the upgrades.

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Quick reference table

Where each key is and what it opens

Lowmarsh Landing (2 keys)

The Rusted Gate Key drops from the first Brine Hound encounter on the main path — you cannot miss it. It opens the chained gate at the north end of the dock district, which is the only route into the First Causeway. If the gate is already open, you picked the key up without noticing; check your inventory under Quest Items.

The Salthouse Key is the first optional pickup. It sits on a crate ledge behind the Salthouse, reachable only by climbing the stacked barrels on the east wall. The key opens the interior storage room, which holds two Weapon Shards and a stack of 40 Tallow. This is the single best early power spike in the game, and per the developers’ launch patch notes it is intended as a reward for exploration rather than a required item.

First Causeway (2 keys)

The Tidewrit Key is found inside the flooded customs house. Drain the lower room by pulling the two wall levers, then swim to the back alcove — the key is on a desk above the waterline, so you need the short climb rather than a dive. It operates the floodgate control panel, which permanently lowers the water level across the whole causeway. Doing this before exploring the side tunnels saves roughly 20 minutes of backtracking.

The Warden’s Key hangs on a hook in the watchtower, guarded by two shielded enemies. It opens the Warden’s cache one room over, containing a weapon mod and a stamina upgrade.

Sunken Chapel (2 keys, both missable)

This is where the run gets fragile. The Anchor Chain Key is recovered from a side chamber that only becomes accessible after you ring the chapel bell. Ring the bell, take the key, and use it on the lift mechanism to reach Mid-Reef. If you leave the chapel via the flooded stairwell instead of the lift, you cannot return — the stairwell collapses behind you.

The Reliquary Key requires the same bell. It is hidden in the confessional booth, behind a breakable panel that is easy to walk past. It opens the Reliquary vault for a lore entry and one Attribute Shard. Grab both chapel keys before you take the lift.

Mid-Reef (2 keys)

The Brineworks Key is a drop from the Brineworks foreman, an optional mini-boss in the pumping station basement. It opens the side door into the upper works, letting you skip two elite encounters entirely. On a no-hit run this is the most valuable key in the region.

The Cartographer’s Key is a puzzle reward: light the four beacon braziers in the correct order, which is shown on a mural in the same room (left, top, right, bottom). It opens the map room, which reveals every uncollected key marker across all regions. If you are chasing 12/12, do the Cartographer’s Key before anything else in Mid-Reef.

Drowned Cathedral (3 keys, one missable)

The Vestibule Key is directly on the entry path — impossible to skip. It opens the safe room beside the nave, which is your only rest point in the region.

The Drowned Bell Key is missable. It is found by swimming down the flooded crypt, and the crypt seals after you trigger the Cathedral descent sequence. Complete the crypt before interacting with the main altar. The key opens the bell tower descent, a shortcut that bypasses about 15 minutes of navigation on any return trip.

The Choir Loft Key sits on the loft railing after you cross the collapsing beams. It opens the loft chest, which contains a cosmetic armour set only — no stats.

The Trench (1 key, plus retroactive unlocks)

The Abyssal Master Key is the final key, awarded for defeating the Trench Sentinel in the arena at the region’s lowest point. Beyond opening the final vault, it retroactively opens the Salthouse storage, the Warden’s cache, and the Reliquary vault if you somehow reached the end without them. It does not retro-open doors in the Sunken Chapel or the Cathedral crypt — those stay locked.

Efficient collection routes

The 100% route (about 85 minutes of travel)

Follow this order and you will never backtrack: Lowmarsh Landing (Rusted Gate, then Salthouse) → First Causeway (Tidewrit, then Warden’s while the water is still high) → Sunken Chapel (bell first, then Anchor Chain and Reliquary together) → Mid-Reef (Cartographer’s puzzle before Brineworks) → Drowned Cathedral (crypt for the Drowned Bell Key before touching the altar, then Loft and Vestibule) → The Trench.

The critical constraint is that the Cartographer’s Key must be obtained before you enter the Cathedral, because it is the only way to see the Drowned Bell Key marker on your map. Players who skip it and dive blind typically finish at 11/12.

The speedrun route (about 40 minutes, 6 keys)

If you only want the upgrades: Rusted Gate, Salthouse, Tidewrit, Warden’s, Anchor Chain, and Abyssal Master. That set gives you the two Shards, the weapon mod, the stamina upgrade, and the final vault, and it skips every cosmetic and lore door. Note that the Abyssal Master Key will retro-open the doors for the keys you skipped, so you lose nothing except the two missable chapel and crypt pickups.

Common mistakes

• Taking the chapel stairwell instead of the lift. This is the most common soft lock for key collectors and costs you two keys permanently on that save.
• Triggering the Cathedral altar early. The descent sequence seals the crypt. Do the crypt swim first, every time.
• Ignoring the beacon puzzle order. The mural is the only hint; the correct sequence is left, top, right, bottom. Random order simply resets the braziers.
• Assuming the Master Key fixes everything. It covers three doors, not the chapel or crypt. Those two must be earned in place.
• Selling keys. They cannot be sold from Quest Items, but players occasionally miss that regional keys sit in a separate tab from consumables — check both before assuming you lack one.

Which keys actually matter

If you are short on time, the ranking is straightforward. The must-have keys are Salthouse, Warden’s, Anchor Chain, and Abyssal Master — between them they hold every permanent upgrade in the game, roughly a 15% boost to total character power by endgame. The convenience keys are Tidewrit and Brineworks, both saving 15–20 minutes of traversal. The skip keys are Choir Loft and Reliquary if you do not care about cosmetics or lore, though Reliquary also carries an Attribute Shard, which nudges it into the useful tier.

Frequently Asked Questions

How many Abyssus Keys are there in total?

There are 12. Nine unlock meaningful content — upgrades, shortcuts, or the final vault — and three open only cosmetic or lore rooms. Only the Drowned Bell Key, Anchor Chain Key, and Reliquary Key are permanently missable, all tied to one-time story gates.

Which Abyssus Keys are missable?

The Anchor Chain Key and the Reliquary Key both require you to use the chapel bell and then leave via the lift; taking the stairwell collapses the route behind you. The Drowned Bell Key is lost if you trigger the Cathedral descent before swimming the crypt. Every other key can be collected at any point, including after the final boss.

Does the Abyssal Master Key unlock everything?

No. It retroactively opens the Salthouse storage, the Warden’s cache, and the Reliquary vault, plus the final vault itself. It does not open the Chapel lift or the Cathedral crypt, so the two missable keys cannot be recovered through it.

What order should I collect the keys in?

Collect the Cartographer’s Key in Mid-Reef before entering the Drowned Cathedral, because it is the only way to see remaining key markers on your map. Otherwise the natural region order works fine as long as you handle the chapel keys before the lift and the crypt key before the altar.

Do I need all 12 keys for the true ending?

No. The true ending requires the Abyssal Master Key and the final vault, which is available with as few as six keys collected. Completion tracking for 12/12 is a separate achievement and does not change the ending.

Can I go back for keys after finishing the story?

Yes for all non-missable keys — post-game free roam keeps every region open. The three missable keys are gone for good on that save, so if you want 12/12 you will need to start a new run and prioritise the chapel bell and the crypt swim early.