Discovering Cobblemon's Ancient Structures
Cobblemon introduces various ancient structures to the world, offering unique exploration opportunities. These structures can contain gilded chests, which may hold valuable loot or other surprises.
Crumbling Arch Ruins
Crumbling Arch Ruins generate in cave biomes. The game attempts to place one of these structures within every 15x15 chunk region. Each generated structure is at least 5 chunks away from any other Crumbling Arch Ruins.
Decaying Crypt Ruins
Decaying Crypt Ruins appear in floral biomes. The game attempts to place one of these structures within every 30x30 chunk region. Each generated structure is at least 13 chunks away from any other Decaying Crypt Ruins.
Desert Structures
Several structures are found specifically in biomes containing sand blocks. These include the Deserted Gimmi Tower, Deserted House Ruins, Deserted Tower Ruins, and Deserted Town Center Ruins.
Deserted Gimmi Tower
The Deserted Gimmi Tower generates in biomes with sand blocks. The game attempts to place one of these structures within every 40x40 chunk region. Each generated structure is at least 25 chunks away from any other Deserted Gimmi Tower.
Deserted House Ruins
Deserted House Ruins appear in biomes with sand blocks. The game attempts to place one of these structures within every 30x30 chunk region. Each generated structure is at least 13 chunks away from any other Deserted House Ruins.
Deserted Tower Ruins
The Deserted Tower Ruins generate in biomes with sand blocks. The game attempts to place one of these structures within every 30x30 chunk region. Each generated structure is at least 13 chunks away from any other Deserted Tower Ruins.
Deserted Town Center Ruins
Deserted Town Center Ruins are found in biomes with sand blocks. The game attempts to place one of these structures within every 30x30 chunk region. Each generated structure is at least 13 chunks away from any other Deserted Town Center Ruins.
How many there are
Cobblemon places 48 structures in total, so the ruins listed above are a sample of a much larger set spread across the Overworld's biomes. They fall into recognisable families — arch and crypt ruins, desert structures, deserted towers and town centres — and members of a family tend to share both their loot table and their construction, which means learning one teaches you what to expect from the rest.
What to take from them
Gilded chests are the reason to clear a structure. They hold the items the mod does not let you craft: 
Ability Capsule and 
Ability Patch for changing what a Pokémon can do, held items, and fossils. Since ability items are otherwise unobtainable, structure exploration is not an optional side activity — it is the supply line for team building.
Reading a ruin before entering
Most of these are surface structures and can be scouted from outside. Look for the chest positions rather than the shape: ruins are frequently partially buried, and the useful half of a deserted town centre may be underground while the visible half is empty. Clearing the exterior first and then digging down along a wall is faster than tunnelling in blind.
Combining trips
Because ruins and the fossil-bearing prehistoric locations are both surface features, a single overland expedition can cover both. Carry a brush for suspicious blocks alongside whatever you use to open chests, and a trip that was going to be structure loot comes home with fossils as well.
Covers the mod’s in-game guide topics: Crumbling Arch Ruins Decaying Crypt Ruins Deserted Gimmi Tower Deserted House Ruins Deserted Tower Ruins Deserted Town Center Ruins
Gilded Chest