We explore new interactions for wayfinding in complex, hazardous environments through the concrete case of multi-pitch rock climbing. Working with seven expert climbers, we derived design principles for navigation tools that support both pre-climb planning and on-the-wall decision making with limited physical and mental bandwidth. We then demonstrate these principles in practice through the creation of a mobile application that incorporates high-fidelity vertical terrain models, spatially-anchored multi-modal annotations, integrated human-scale avatars, and adaptable one-handed interactions. Based on our expert feedback and experiences developing the tool, as well as results from a 3-week public deployment and responses from 16 climbers, we highlight new opportunities for interactive tools for rock climbing as well as other hazardous, high-focus activities.