Hinterlands

A Russian space mission vanishes in mid-flight to Mars and reappears two years later. When a rescue mission reaches the ship, they find the cosmonaut dead but a seashell grasped in her hand. What follows is the discovery of a passage to another place, where the technology isn't necessarily more advanced but just very different from our Universe. All future missions fail to bring back any digital data, only handwritten notes survive, and the mission crews come back dead or insane. This sets the stage for an intense mystery of what lies on the other side.