SPOILER: The endings of the US and UK versions differ. In the end, Sarah wakes up at the bottom of the cave, crawls out, and makes her way back to the car. When she is driving away, she pulls over and vomits, and when she leans back into the car, she is startled by the ghost of Juno sitting in the passenger seat. The US version cuts to the credits here. In the UK version, this apparition causes Sarah to wake up for real at the bottom of the cave, revealing her escape to be just a dream. She then has a vision of her daughter's birthday cake, which we see is just her torch. The camera backs out, the voices of the creatures can be heard again and are increasing in strength as they are closing in on her, and the movie ends. This ending was considered "too dark" for US audiences.
In the alternate version of the movie, Sarah escapes the cave and runs to her car. She drives down the road and stops. After vomiting out the window, she sits up and Juno, whose face is streaked with blood, is sitting right beside her. Sarah screams and the camera cuts to the credits.