City-building sim Cities: Skylines is getting its first expansion pack, and it's one based around the addition of a nighttime period for your cities.

The day-and-night cycle is the primary new feature revealed today as part of the After Dark expansion, and it's something that all users will receive in a free update coming at the same time as the expansion. This is more than just a cosmetic change, as cities functions differently at night. Citizens do different things, there's less traffic, and certain areas (depending on their zoning) are less effective.

After Dark also adds a leisure specialization for commercial areas, which will be busier at night but work normally during daytime hours. Alongside this is the new beach specialization, which wasn't specifically said to operate differently throughout the day, but presumably will.

City services are being expanded with taxi service for citizens and tourists, prisons for criminals to be taken to from police stations, international airports (increasing the amount of airport traffic you can receive), and bus terminals that transfer citizens from one bus line to another.

New transportation options include bikes (along with dedicated bike lanes and paths), as well as dedicated bus paths that can help public transportation to operate more efficiently.

After Dark doesn't yet have a release date or a price, nor do we know if this content will also be available for the recently revealed Xbox One version. We followed up with Paradox, but it didn't have any information to share about the possibility of a console version of After Dark.

Skylines debuted earlier this year and was a quick success, selling more than 1 million units in its first month alone. Those sales figures surprised even its developer, which has pledged new free and paid content for the game that continues to have a robust modding community.