A composite structure comprising: a first outer skin; a second outer skin; and a core sandwiched between the first outer skin and the second outer skin; wherein the core comprises: a plurality of spaced apart ridges between the first outer skin and the second outer skin, each of the spaced apart ridges extending from one end of the composite structure to an opposite end; and a plurality of connecting elements between the first outer skin and the second outer skin intersecting with the ridges to form open channels within the core; characterised in that the ridges of the core and the connecting elements of the core each comprises a plurality of composite plies including at least a first composite ply and a second composite ply, the first composite ply and the second composite ply each comprising a plurality of unidirectional, continuous parallel fibers in a thermoplastic matrix, the plurality of composite plies being bonded together to form a composite laminate; and both the first outer skin, and the second outer skin comprise: a plurality of composite plies including at least a first composite ply and a second composite ply, the first composite ply and the second composite ply each comprising a plurality of unidirectional, continuous, parallel fibers in a thermoplastic matrix; the plurality of composite plies being bonded together to form a composite laminate, and wherein the plurality of fibers in the first composite ply are parallel to each other, and the plurality of fibers in the second composite ply are parallel to each other, wherein the plurality of fibers in the first composite ply are disposed cross-wise to the plurality of fibers in the second composite ply at an angle of greater than 0 degrees to 90 degrees, and wherein the plurality of fibers in the first composite ply are different from the plurality of fibers in the second composite ply. a first outer skin; a second outer skin; and a core sandwiched between the first outer skin and the second outer skin; wherein the core comprises: a plurality of spaced apart ridges between the first outer skin and the second outer skin, each of the spaced apart ridges extending from one end of the composite structure to an opposite end; and a plurality of connecting elements between the first outer skin and the second outer skin intersecting with the ridges to form open channels within the core; characterised in that the ridges of the core and the connecting elements of the core each comprises a plurality of composite plies including at least a first composite ply and a second composite ply, the first composite ply and the second composite ply each comprising a plurality of unidirectional, continuous parallel fibers in a thermoplastic matrix, the plurality of composite plies being bonded together to form a composite laminate; and both the first outer skin, and the second outer skin comprise: a plurality of composite plies including at least a first composite ply and a second composite ply, the first composite ply and the second composite ply each comprising a plurality of unidirectional, continuous, parallel fibers in a thermoplastic matrix; the plurality of composite plies being bonded together to form a composite laminate, and