Mazes

Mazes are an object/concept that crossover between the two initial concepts. It touches on the ideas of boundaries, the way that from the outside a maze is just a giant box, but on the inside it's very complicated and you can only find this out by crossing the 'boundary' / the entrance to the maze.
It also controls you (masochistic) and only allows you to go certain ways. The maze is in control (master/slave dichotomy).