A multi-sensory cognitive engagement puzzle device for stress reduction, mindfulness, and dementia therapy is disclosed. The device includes a three-dimensional geometric puzzle structure composed of interlocking posts, wherein each post comprises a plurality of interlocking puzzle pieces, wherein the puzzle pieces comprising center puzzle pieces, middle puzzle pieces, external puzzle pieces, wherein each puzzle piece having protrusions, indented sections, grooves configured along at least one of protrusions and indented sections, and magnets, wherein the indented sections are configured to form a continuous outer surface when fully assembled to form the post, and wherein magnets are integrated into grooves of either protrusions and indented sections and configured to slide and lock into, during assembly, either protrusions and indented sections and along each post and between adjacent posts. The surface of each puzzle piece comprises textures distinct to each other to provide distinct tactile sensations.

A pickagram three-dimensional puzzle comprises seven 3D blocks and a plurality of magnetic members located inside each 3D block to couple the neighboring 3D blocks to one another through magnetic forces generated therefrom. A first 3D block of the seven 3D blocks has the shape of a right triangle on a plane and include a first top face, a first bottom face located to be opposite to the first top face, a first lateral face for connecting the boundary edges of the first top face and the boundary edges of the first bottom face to one another, and a plurality of accommodation pipes arranged along the first lateral face, and the plurality of magnetic members include a plurality of first magnetic members located correspondingly inside the plurality of accommodation pipes.

A multi-component structure comprising complementary segments and the multi-component structure comprises a first complementary segment having a first convex portion and a first concave portion. The first convex portion is contiguous with the first concave portion. The multi-component structure further comprises a second complementary segment and a second convex portion, the second concave portion being contiguous with the second convex portion, the second concave portion sized to be received within the first convex portion and the second convex portion that is sized to be received within the first concave portion. When the first complementary segment and the second complementary segment are releasably secured to one another, the two segments form a first hemisphere.