Dimension is a city builder game that, in contrast to normal city builders, makes use of the upwards/downwards directions during construction.
The player is given a relatively small cube or sphere shaped world to build on, where roads will seamlessly transition across any edges. This creates an internal area of land for the player to use to build tunnels between any area of any edge. Immediately the player has a new way of managing traffic, and a lot more space to funnel cars in. Cars are able to follow 'tunnels' regardless of the direction of gravity, though gravity always pulls perpendicular to the faces but inwards to the centre of the world.
In addition to building within the centre of the world, the player can build upwards from the faces. With adequate support, buildings and zones can be placed above others. This is not always a beneficial thing however, as airplanes still need to have a path to airports and emergency vehicles quick access to all buildings.
The biggest challenge - similar to most city builders, comes from managing the additional density created by using the vertical direction, which compensates for the additional ways to move traffic.
Image source W.H. Corbett, retrieved 25/07/2016 from https://blog.inpolis.com/2012/07/02/guest-article-skywalks-in-hong-kong-and-their-consequences-on-urban-communities/