Making virtual metropolises is fun until you start thinking about all of the virtual pollution you’re creating. Cities: Skylines’s next expansion, Green Cities, looks to ease your conscience when it comes out on October 19 for PC for $13.

Cities: Skylines has sold more than 4 million copies. The city simulator was able to take advantage of a market void when 2013’s SimCity disappointed fans with its size limits and always-online requirements. Cities: Skylines came out for PC in 2015, and PlayStation 4 and Xbox One versions followed this year. Green Cities does not have a release date on consoles yet.

Expansions are an important part of keeping players engaged for games like this. The new content gives them incentive to keep playing, plus that $13 price point gives Cities: Skylines a way to make money off of people who already bought it.

This is the fifth major expansion for Cities: Skylines following After Dark, Snowfall, Natural Disasters, and Mass Transit. Green Cities adds 350 new assets, including buildings, parks, and city services.

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