The ocean monument is constructed entirely from variants of prismarine and lit by sea lanterns. It includes a large central section flanked between two wings. Under the monument are 23 giant pillars that stretch to the ocean floor. The main entrance is located at the front of the central section.
The central section consists of various types of chambers forming a randomly-generated maze. The chambers connect vertically and horizontally to the different parts of the monument, including the left and right wings. In the topmost room and in each wing reside elder guardians. In the back of the central section lies the treasure chamber, a tall room with eight gold blocks encased in dark prismarine.
The basic unit in the monument is an 8×8×4 "small room". The larger rooms, excluding the penthouse and wings, are made of combinations of these smaller rooms.
- Wings extend from the front of the body of the monument, and connect via a passageway around the bottom of the body of the monument. One wing has a large room with a pillar, while the other consists of a large open area. Each wing contains an elder guardian.
- The penthouse is in the very top of the monument, and contains an elder guardian.
- The core is made up of 2×2×2 basic units, and contains 8 gold blocks wrapped in dark prismarine.
- The entry room is always at the bottom front center, opening to the ocean outside the monument.
- DXY rooms, 2×1×2 basic units, have two hollow pillars coming up with openings in each facing the top-center and four sea lanterns at corners beneath the openings.
- DYZ rooms, 1×2×2 basic units, are largely open rooms with a 2×2 pillar made of dark prismarine and sea lanterns in the middle. Openings in the top of the left and right walls have a ledge with a frame around the potential lower openings.
- DZ rooms, 1×2×1 basic units, have an open-centered structure made of prismarine bricks in the middle, with sea lanterns on the four corners.
- DX rooms, 2×1×1 basic units, are U-shaped: one wall has an outcropping consisting of a 6×4 rectangle of prismarine bricks on the floor and ceiling with a 4×3 rectangle of prismarine with sea lanterns at the corners in the middle.
- DY rooms, 1×1×2 basic units, are tall rooms with 2×2 corners of prismarine bricks midway up, each with the piece in the corner of the room missing. Open walls have insets in the side such that two of these rooms adjacent will have additional 2×1 openings on either side of the usual passageway.
- Sponge rooms, 1×1×1 basic unit, have openings only to the bottom. Each of the 36 columns in the room has a 1⁄3 chance of being empty, a 1⁄2 chance of having one sponge, and a 1⁄6 chance of having two sponges. The walls have dark prismarine.
- Small rooms, 1×1×1 basic unit, made plus-shaped by 2×2 prismarine bricks at floor and ceiling in each corner, with sea lanterns in the four corners at the middle level.
- Small rooms, 1×1×1 basic unit, with four 1×1 pillars of prismarine brick and sea lantern. If both the top and bottom walls are closed and at least two other walls are open, has a 50% chance of having a 2×2 pillar in the middle.
- Small rooms, 1×1×1 basic unit, normally empty with dark prismarine on the walls. If both the top and bottom walls are closed and at least two other walls are open, has a 50% chance of having a 2×2 pillar made of prismarine and prismarine bricks in the middle.
- It starts with 49 basic units: two layers of 20 (5×4) with one layer of 6 (3×2) on top, plus 3 dummy units representing the wings and the penthouse. Every unit connects to all adjacent units (up, down, left, right, forward, and back, including connections with the dummy units), and all the walls between connected units are initially marked as "open". The 46 non-dummy units are marked as "unused", while the dummy units are "used".
- The core is placed somewhere at the back of the monument. The 8 units taken up by the Core are marked as "used".
- If the core is at the far left or far right, it will open into the passage connecting the two wings.
- The list of units is randomized, and for each unit up to 5 attempts are made to close walls until two closures succeed:
- A direction is chosen: up, down, left, right, forward, or back.
- If the wall in that direction is already closed, the attempt fails.
- The wall is marked as closed.
- The two units on either side of the just-closed wall are checked to make sure a path through open walls still exists from each one to the entry unit. If either fails, the wall is re-opened and the attempt fails.
- Place the entry room, marking that unit as used.
- The randomized list of units is gone through again to choose what size monument room will be placed for each one that is still unused. The first option that fits is applied:
- If the walls between the current unit, the one above, the one to the right, and the one above and to the right are all open and all those units are still unused, place a DXY room (marking the 4 as used).
- If the walls between the current unit, the one above, the one to the back, and the one above and to the back are all open and all those units are still unused, place a DYZ room (marking the 4 as used).
- If the wall between the current unit and the one behind is open and the one behind is still unused, place a DZ room (marking both as used).
- If the wall between the current unit and the one to the right is open and the one to the right is still unused, place a DX room (marking both as used).
- If the wall between the current unit and the one above is open and the one above is still unused, place a DY room (marking both as used).
- If all walls except the bottom are closed, place a sponge room.
- Otherwise, place one of the three small rooms (1⁄3 chance of each).