The Atomic Heart ballerina puzzle comes at the culmination of your time at the Theatre, and serves as the final barrier standing between you and Petrov. Specifically, you must solve it in order to progress past the 'Ascending the (Gallows) Stage' objective, which challenges you to find a way to open the gate.
Starring some thematically appropriate shadow puppetry, the Atomic Heart ballerina puzzle is markedly different from the usual brand of puzzles you'll come across in the FPS game, and its environmental signposting can easily go overlooked. Here's how to solve it and progress through Facility 3826.
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