Land of the Lost (1974)

Widowed forest ranger Rick Marshall and his two children, Will and Holly, are enjoying a rafting trip when they accidentally fall over a waterfall. However, instead of being killed they somehow fall through a dimensional doorway into a closed universe populated by dinosaurs, ape men known as Pakune and a race of lizard like men known as Sleestacks. The Marshalls make the most of their time there as they try to find a way home for the next two years by using a monolithic chamber known as a pylon which acts as a doorway to other worlds. However, one day Rick tries to use one of them to try to get back home and disappears. However, Rick's brother Jack who has been searching for them lands in the Land of the Lost and joins his nephew and niece in trying to get back home.