The ability to navigate efficiently is fundamental to animals’ survival and success; enabling them to find mates, avoid predators and find their way home. To orient around their local environment, animals must recognise their own position with respect to a goal. This task can be achieved through a representation of space in their brain, built upon learning and remembering environmental features that are inputted through multiple sensory systems. A substantial research effort has sought to understand how animals navigate, but this has been focused on horizontal movement, despite the real world being three-dimensional. Indeed, most animals have some kind of vertical component to their movements, and there are both quantitative and qualitative reasons why navigating through environments with a vertical axis might be different to navigating purely in 2D. This is pushed to the extreme in volumetric environments, such as those inhabited by many fish. By using experimental and theoretical approaches, we consider how pelagic and benthic fish deal with 3D navigation; from the sensory input, to what information is learned and remembered. This not only allows us to unpick the mechanisms that underpin this important behaviour, but can also inform us about the processes behind learning and memory themselves.