Something of a tour de force, this adaptation of Joe Simpson’s nonfiction book about his climbing the 21,000-foot Siula Grande mountain in Peru, breaking a leg, and eventually making it back alive is remarkable simply because the story seems unfilmable. Director Kevin Macdonald has Simpson and his climbing partner, Simon Yates, recount most of their adventure in a London studio; selected bits of action are restaged on location in the Andes and Alps, using actors Brendan Mackey and Nicholas Aaron as well as the original participants, while the restwhich is a lotis left to the viewer’s imagination. The monumental settings and the hallucinatory treatment of time, which seems increasingly stretched out toward the end, are both capably handled. 106 min. (JR)