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Scenarios › Isles of Abyss › Calamity Tower & Nest

Once Human Calamity Tower & Calamity Nest Guide

LiveUpdated 2026-10-23 · Game v3.1.1Sea boss and land stronghold

By the Once Human Guide crew — a small fan team led by Yao · from patch notes + videos

Short answer: In Isles of Abyss, a Calamity Tower is a lighthouse-like boss at sea that you fight from your ship: shoot the weak points on its tentacles with your cannons. It comes as a solo story fight, a team fight and, in Phase II, Calamity Tower: Abyss. A Calamity Nest is a land stronghold whose boss, the Calamity Owl, summons enemies with its song and marks one player for Revenge.

On this page
  1. Not the older Calamity Tower
  2. Calamity Tower vs Calamity Nest
  3. How to beat a Calamity Tower
  4. How to beat a Calamity Nest and the Calamity Owl
  5. Rewards
  6. More for Calamity fights
  7. FAQ
  8. What changed

Not the older Calamity Tower

Search results for “Once Human Calamity Tower” also show older database pages with titles like “Calamity Tower - Return to Abyss Lv.50” and “Calamity Tower - Burning Grudge Lv.60”, plus an item called “Calamity Tower - Gaze”. They appear to be separate, older content that shares the name; what they are exactly is not confirmed here. This page covers only the Isles of Abyss sea tower and land nest. Note that the scenario’s own hard mode is called Calamity Tower: Abyss, which is not the same name as “Return to Abyss”.

Calamity Tower vs Calamity Nest

Calamity Tower Calamity Nest
where at sea, anchored in the ocean on land, after you go ashore
boss the tower itself: tentacle arms and a central eye Calamity Owl
you fight with ship cannons your own weapons, solo or in a team
tiers solo story → team → Calamity Tower: Abyss (Phase II) difficulty rises with more summons and skill combos
key mechanic tentacles block areas, summon help, heal and share damage; defensive structures protect them song summons enemies; sound-wave attacks; Revenge marks one player
Morphed Deviations Shattered Maiden - Sailor Suit · Gingerbread House - Oceanic Cottage Snow Globe - Sunken Treasure

src: patch notes (2026-10-21) · dev blog (2026-10-16) · momsbisburi ZHiW-FU_tCU @06:01–06:21

How to beat a Calamity Tower

  1. The fight eats ammunition. One test-server guide waits until it has its tier-two gear and a ship stocked with cannonballs before attacking the first tower. test server Towers switch on gradually as world progress advances, so you may see one before you can fight it.

    src: Gotcha Beast KJvFq__cWp8 @07:01 (test server)

  2. The developer recommends the Rapid-fire Cannon for tower weak points. One creator prefers the Long Cannon instead: slower, but each shot hits hard, and he repositions between shots. Which cannons do what: Ship cannons.

    src: dev blog (2026-10-16) · Grizl o5-Cq9fuLF0 @05:40

  3. The tentacles are covered by defensive structures, and ship cannons do the real damage to them. Some tentacles wall off areas, call reinforcements, heal the tower or spread damage between them, so remove those first.

  4. Each arm has a glowing weak point. Keep firing at those until every tentacle is severed.

  5. With the tentacles down, focus all fire on the big eye in the middle of the tower.

    src: Gotcha Beast KJvFq__cWp8 @07:01 (test server) · Doomeris zIDlwmX7CPg @18:20

Calamity Tower: Abyss (Phase II)

After the required trials in Phase II you can push deeper into the tower. At this difficulty the tentacle abilities stack, the core attacks on its own, and Voyager ships join as reinforcements. Waves, thick fog, icebergs and waterspouts also get in your way, so keep the hull in good repair and plan your escape route. Fog and cold gear: Haywire Zones. Fixing and steering the ship: How to build a ship.

src: patch notes (2026-10-21) · momsbisburi ZHiW-FU_tCU @06:21

How to beat a Calamity Nest and the Calamity Owl

Nowl
Calamity Owl
attacks
Its song calls enemies to it, and it keeps up pressure with sound waves and area attacks
Revenge
The Owl marks one player. Enemies chase whoever is marked, but the mark is also that player’s chance to hit the Owl, so the rest of the team covers them
counter
Pick up fallen feathers to lift off briefly, and touch the floating energy orbs to strike back
harder
Higher difficulty brings more summoned enemies and tougher skill combos
why bother
One test-server guide says Owls are needed for story progress, Nests appear in random spots, and the Owl is one of two sources of top-tier cannons test server

src: patch notes (2026-10-21) · Doomeris zIDlwmX7CPg @19:00 · Gotcha Beast KJvFq__cWp8 @12:39, @14:22 (test server)

Rewards

  • Heart of the Ocean is spent at the Calamity Tower reward stage to open challenge rewards, including the new Precision Load (lower-body mod: hitting weak points at range returns ammo) and Turret Enhancement (gloves mod: more damage from facilities you operate, such as cannons).
  • Morphed Deviations: Shattered Maiden - Sailor Suit and Gingerbread House - Oceanic Cottage from Calamity Tower; Snow Globe - Sunken Treasure from Calamity Nest.
  • First tower kill: a reward mail for the whole server and a push in World Progress toward Phase II, according to the developer’s test-recruitment post.
  • Drop rates are not confirmed yet.

src: patch notes (2026-10-21) · Final Test Recruitment post (2026-08-28)

Phase II also adds the Sea Calamity Zone, where you destroy shield cores to reach a Calamity Hatchling. A Calamity Hatchling also guards the entrance to the final boss: The Sunken Lord.

More for Calamity fights

FAQ

How many Calamity Towers are there?
Not confirmed yet. One creator on an early-access server counted five across the island regions. The developer hasn’t published a number, or whether each sea has exactly one.
Do I have to beat Calamity Towers to progress?
They are part of the main story, and the developer’s test-recruitment post says the first kill of a tower sends a reward mail to the whole server and pushes World Progress toward Phase II. A test-server guide adds that it unlocks the next tier of regional crafting.
Is Calamity Tower: Abyss the same as “Calamity Tower - Return to Abyss”?
Don’t assume so. Calamity Tower: Abyss is the Phase II difficulty of the Isles of Abyss sea tower. “Return to Abyss Lv.50” is the title of an older same-named activity listed on a database site, and how the two relate is not confirmed.
Is the main quest just Owls, ships and towers on repeat?
A Steam thread asked whether the story is “beat the Owl, the ship and the tower three times each, then repeat on four similar islands”. Nobody has answered it, and the developer hasn’t described the quest structure, so this is not confirmed yet.
Can I fight a Calamity Nest solo?
Yes. The developer says you can take it on alone or with a team. The Revenge mark is built around teamwork, though, so it is easier with someone else.

What changed

  • v3.1.1 · 2026-10-23Page created.

Sources

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