The city is built on a hill, with the emperor's tower crowning the peak and standing far above all other buildings. Surrounding the tower are twelve smaller towers, one for each cardinal direction and two in between those four. Stemming from each tower is a road that goes straight down the hill, like the spokes of a wheel. There are also smaller streets in-between.
There are two additional main roads that start at the eastern and western towers and cascade down the hill in a spiral pattern, like the shape of a nautilus (hence the city's name). These are the main roads, and most businesses will be built along there.
Flowing down from the tower and alongside the streets and in between the white houses are little rivulets and streams.
At the intersection of the four cardinal spokes and the the third spiral down of the two main roads are the Plazas: The Plaza of Waterfalls to the east, the Plaza of Whirlwinds to the North, the Plaza of Infernos to the West, and the Plaza of the Fallen. Each Plaza bears sculptures that correspond to their names: swirling spirals in the north, running waterfalls in the east, sculpted flames in the west, and what look like the stumps of magnificent trees in the south.
In addition, the four districts of the city are named thus: Waterfalls, Whirlwinds, Infernos and Fallen, and all buildings and décor bear this motif. Buildings at the top of the hill, closer to the tower, are grander and larger, and they get smaller and more cramped towards the bottom, but remain nice and spacious. Nautilus is a comfortable city.
Interestingly, the architecture varies vastly; while the 'default' is an Art Noveau with Gothic and Greek elements, the shapes of buildings change based on the origins of the city's inhabitants. See the State of the Game posts for more details.
At the edge, there is just a white void. Wandering into this area leaves you with a sense of vertigo, and a strong desire to return to the city. If you continue to press on into the white void, you will slowly lose sense of your body, and feel disconnected from it. this can be corrected by simply willing yourself to return to the city. In addition, if you enter this zone and will yourself home, you will return there instantaneously, but please see the FAQ on returning home for more information.
Currently, there is no marketplace, or any semblance of an economy anywhere. Food can be easily willed into being merely by desiring it; but if that is not desired then there is a large fruit and vegetable garden in the District of the Fallen. In addition, there are a large number of birds throughout the city - mostly pigeons and doves, but also a few falcons, some starlings, and other creatures. Plants of all kinds can be found throughout the city, from many disparate locations - including such anachronisms as palm trees growing next to pine. The vast majority of plants grow in the District of the Fallen and the District of Waterfalls.
Days and nights are technically twelve hours long each. In most of the city, the sky is a clear blue during the day and star-filled at night, with one sun and one moon, save in the District of Infernos, where the sky is red with two small moons at night. In the District of Whirlwinds and wherever Pyramid Head is, there is thick fog during the hours of dawn and dusk.