The Northwest Territories (NWT), Canada has high rates of sexually transmitted infections (STI) that elevate HIV acquisition risks. We conducted a mixed-methods study to explore the potential of land-based peer leader retreats (PLR) in building HIV prevention enabling environments among Northern and Indigenous youth in the NWT. PLRs are grounded in Indigenous principles and ways of knowing, acknowledging the land as a physical, spiritual, emotional, and intellectual being with the potential to facilitate (re)connection to culture, community, and self. We conducted one-week PLRs between 2016 and 2021 with adolescents aged 13-17 in the NWT. PLRs addressed HIV/STIs, safer sex, and gender equity. We conducted post-retreat focus groups (FGs) and pre/post-retreat surveys with youth participants (n = 353), and post-retreat FGs with PLR facilitators (n = 252). We applied thematic analysis to FGs and assessed pre/post-retreat changes in HIV/STI knowledge and safer sex efficacy (SSE) using paired sample t-tests. We assessed factors associated with post-test SSE and HIV/STI knowledge using multivariable linear regression. Youth participants (n = 353; mean age: 14.5, standard deviation [SD]: 1.3) were mostly Indigenous (71%) and women (66%). Participant narratives revealed PLRs enhanced technical communication (e.g., correct condom use). There were significant post-retreat HIV/STI knowledge increases; change score increases were lower for Indigenous participants. Qualitative narratives described how PLRs fostered transformative communication (e.g., sexual consent). There were significant post-retreat increases in SSE, and these were lower among men and sexually diverse (vs. heterosexual) participants. Land-based PLRs offer the potential to build technical and transformative communication to facilitate HIV prevention with youth in Canada's North.