Designing software for exploring hierarchical data sets is challenging because users can easily become lost in large hierarchies. We present a novel interface, the hoptree, to assist users with navigating large hierarchies. The hoptree preserves navigational history and context and allows one-click navigation to recently-visited locations. We describe the design of hoptrees and an implementation that we created for a tree exploration application. We discuss the potential for hoptrees to be used in a wide variety of hierarchy navigation scenarios. Through a controlled experiment, we compared the effectiveness of hoptrees to a breadcrumb navigation interface. Study participants overwhelmingly preferred the hoptree, with improved time-on-task with no difference in error rates.