In the first "Pacific Rim" film, the Kaiju -- interdimensional monsters who emerged from a portal in the Pacific Ocean -- were defeated by a group of international Jaeger pilots. Though many of the plot details for "Pacific Rim: Maelstrom," the followup to the 2013 cult classic film, remain under wraps, director Steven S. DeKnight unveiled a new mystery in a post on his Instagram.

"What's behind this awesome door? You'll have to see 'Pacific Rim 2' to find out," he captioned the post.

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What's behind this awesome door? You'll have to see #PacificRim2 to find out. #onset

A photo posted by Steven S. DeKnight (@stevendeknight) on

Of course, since so little is known about the film, it's hard to even begin to speculate what's behind that door. Seeing as the Kaiju were defeated, though, it's not a stretch to guess that it may contain a new threat against our Jaeger pilots. One thing is clear, though: we won't find out until the film hits theaters in February 2018.

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In the first film, Charlie Hunnam's Raleigh Becket -- a former Jaeger pilot -- was forced back in the saddle when the threat of the Kaiju intensified. Enlisted once more, he found himself paired with Mako Mori (Rinko Kikuchi), a trainee getting her first shot at piloting. Under the direction of Idris Elba's Stacker Pentecost, Becket and Mori joined humanity's last stand against the Kaiju, only to be successful when scientists Dr. Newton Geiszler (Charlie Day) and Gottlieb (Burn Gorman) stumbled upon the monsters' weakness.

Shooting for “Pacific Rim: Maelstrom” began earlier this month in Australia. Further scenes will also be shot in China. Although few plot details have been released, it was announced that John Boyega will play the son of Stacker Pentecost. Photos of Boyega in costume recently surfaced on Twitter.

In addition to Boyega, Scott Eastwood and Cailee Spaeny also star. Jing Tian (“The Great Wall,” “Kong: Skull Island”), Wesley Wong (“Transformers 4”), Zhang Jin, Lily Ji, Chen Zitong, Lan Yingying and Qian Yong Chen have recently joined the cast as well.

Directed by Steven S. DeKnight and written by Guillermo del Toro, Zak Penn, Jon Spaihts, Derek Connolly, Emily Carmichael, Kira Snyder and T.S. Nowlin, “Pacific Rim: Maelstrom” will hit theaters on February 23, 2018.