Last Minute Preparations

You need a Cyclops for deep exploration as the Seamoth's 900m depth limit is insufficient. The Prawn Suit can reach 1700m but lacks mobility.

If you lack Cyclops Hull Fragments, search the Mushroom Forests or Sea Treader's Path.

If you lack Cyclops Engine Fragments, search the Mushroom Forests, Underwater Islands, or Crash Site.

If you lack Cyclops Bridge Fragments, search the Mushroom Forests, Sea Treader's Path, or Crash Site.

Once you have a Cyclops, familiarize yourself with its operation and reactions to emergencies.

Craft upgrade modules for your Cyclops.

Use your Habitat Builder to create base objects inside the Cyclops, turning it into a mobile base.

Craft the first Cyclops depth module. If you don't have the blueprint, find Lifepod 2 in the northern Blood Kelp Zone for a databox.

Consider crafting the Reinforced Dive Suit from a databox. It reduces damage taken and increases survivable temperatures outside a vehicle.

Bring a knife.

Upgrade your Prawn Suit with new arms. The default arms can pick up objects and punch.

Craft a Drill Arm for your Prawn Suit to mine large ore deposits and nodes found in the deepest reaches.

Bring two pots with plants like bulbo trees for a sustainable food and water source within the Cyclops, as underground areas lack water-producing fish. Alternatively, stock a large amount of water from your base.

Build a Fabricator and a Modification Station inside your Cyclops.

Bring materials to construct a small base with a moonpool and vehicle upgrade console to craft the Prawn Suit MK1 depth module, as one required material is found early in the deep journey.

Bring materials for the Prawn Suit MK2 and MK2/3 Cyclops depth upgrades. Nickel and kyanite are found deeper.

Bring extra power cells for the Cyclops, as energy consumption will be high.

Craft two Purple Tablets or bring the materials to make them.

Place beacons to navigate the potentially maze-like deep areas, as the Pathfinder Tool may not suffice for the distances involved.