Landfall’s co-op climbing game, Peak, achieved significant sales numbers in the past week, selling over one million copies on Steam in six days. Peak became a surprise hit for the Haste and Stick Fight publisher with the game peaking at 102,000 concurrent players on Sunday. Those kinds of numbers topped even recent hits Rematch and Dune: Awakening.

Peak’s gameplay seems simple, but this is hardly Ice Climbers. Players can either do solo or co-op runs as they try to escape a mysterious island by climbing the center of the tallest mountain–which changes each time you play.

As you play, you can help each other up ledges, or place ropes and climbing spikes to make the way easier for those who come after. There are four biomes on your way to the mountain’s peak, each with their own life-threatening obstacles. Climbing isn’t your only objective, though: You’ll need to scavenge for questionable food to survive, and manage your injuries very carefully. Every setback limits your stamina, making it harder to climb.

The game went through some major bug fixes recently, including the tropics crash on AMD hardware. The cause? The grass. So for the meantime, grass is disabled, but could be reintroduced later. A “Lobby Mode” was also slightly changed, so now you can change it to “Invite Only,” which will prevent others from being able to join the game without an invite.

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