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Free modular 3D assets for prototyping
Modular kits let you build levels fast. Free kits worth knowing, how grid sizes work, and when to swap kit pieces for unique props.
3 min read
Quick answer
What are modular 3D assets and where can you get them free?
Modular assets are kit pieces, such as walls, floors, corners, doors and stairs, built to a shared grid so they snap together into many levels. Kenney publishes free CC0 modular kits for dungeons, cities, castles and more, and itch.io and OpenGameArt host others. Engine tools like Unity ProBuilder and Godot CSG can also make quick modular blockouts.
Why modular kits are so useful
A modular kit is a set of pieces designed to fit together on a grid: wall segments, floor tiles, corners, doorways, windows, stairs, pillars. Ten well-designed pieces can build hundreds of rooms. For prototyping, that's ideal: you can try a level layout in an afternoon and change it in minutes.
How the grid works
- Every piece is built to a fixed grid size, for example 1 m, 2 m or 4 m.
- Pivots sit at a corner or edge so pieces snap precisely.
- Heights are consistent so floors and walls line up.
Turn on grid snapping in your engine with the kit's grid size, and pieces click together.
Free kits
- Kenney: several 3D kits built to be modular, such as dungeon, city, castle and space station pieces, all CC0. Kenney's kits are the go-to for game jams.
- Quaternius: some packs include modular building pieces; check licences.
- itch.io and OpenGameArt: search "modular"; licences vary.
Build your own blockout kit in-engine
For greyboxing, you don't need art at all:
- Unity ProBuilder: make walls, floors and ramps inside Unity.
- Godot CSG: combine boxes and cylinders in the editor.
- Unreal's Modeling Mode and its blockout tools.
Make a handful of pieces at your grid size, save them as prefabs or scenes, and you have a custom kit.
From modular prototype to finished level
Kits get you a layout. To make it feel like a real place:
- Lock the layout with the kit.
- Replace hero spots with unique pieces: the entrance, a landmark, the boss room.
- Dress with props that aren't on the grid: furniture, clutter, decoration.
- Vary the repetition with decals, lighting and a few alternate wall pieces.
From greybox to dressed level walks through the swap.
Where AI generation fits (and where it doesn't)
Not for kit pieces. Generated models don't come out on an exact grid with precise edges and pivots, so they don't snap. Model kit pieces by hand or use a kit.
Great for everything around the kit: props, furniture, statues, set dressing, the unique centrepieces that make a level memorable. Generate them in the kit's style, set the pivot at the base, and place them freely. AI 3D props for indie games covers which props generate well.
Tips
- Pick your grid size before anything else and stick to it.
- Name pieces by size and type:
wall_2m_straight,floor_2x2. - Include a few odd pieces (half-walls, angled corners) for variety.
- Test player scale early; doors and corridors must fit the character.
Laid out your level? Generate the props that make it feel lived-in in Vi3W.
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