A user can be authenticated via traversal of a three-dimensional structure and entry of an authentication code. For example, a user-entered authentication code can be compared to an authentication code, and a user-selected element of the structure can be compared to a destination element resulting from following an authentication path through the structure beginning at a starting element. As another example, a user-selected ordered series of elements of the structure and corresponding user-entered sub-codes can be respectively compared to an authentication ordered series of elements of the structure resulting from following ordered steps of an authentication path through the structure beginning at the starting element and to sub-codes of an authentication code.