Cities: Skylines developer Colossal Order was “very surprised” by the fact that the SimCity-like simulation PC game enjoyed such strong sales, reaching 1 million copies sold in one month. In an new interview with TechRadar, CEO Mariina Hallikainen said seeing the game sell so well has also been “very exciting.”

“To be honest I was very surprised because we’re a very small company, and [publisher Paradox] isn’t a massive publisher,” Hallikainen said. “If you think about the budgets for marketing and the game itself, the ability we have is amazing. There’s almost this blurred line between what is creating and what is playing–and people have been sharing their creations with the world.”

Hallikainen pointed out that the Steam Workshop for Cities: Skylines currently has more than 45,000 items, a figure she described as “mind-blowing.”

“It’s definitely something we didn’t see happening so fast. I was hoping that Cities: Skylines might be the game that sells over a million copies in three years or something, and it happened in just over a month,” Hallikainen explained. “It’s very exciting.”

Also in the interview, Hallikainen teased that Colossal Order will announce a “big expansion,” along with some more free and paid content for the game, during Gamescom in August.

For lots more, be sure to read TechRadar’s full interview with Hallikainen.

In GameSpot’s 8/10 Cities: Skylines review, real-life mayor Brett Todd wrote: “Right now, there is no better way to take a peek at life as a mayor without filing your papers to run for office in the real world.”

Meanwhile, SimCity developer Maxis Emeryville has shut down, though support for SimCity and The Sims 4 will continue.