This paper evaluates which processes determine the leverage of cycling tourism trails for mainstreaming cross-border contact and 'soft' region-building. Reflecting on the Vennbahn between Germany, Belgium and Luxemburg, the paper shows that the influence of routes on cross border integration depends on the trail's strength as a tourism product, its cross-border institutionalization, and the geography and scale of the trail and the involved destinations. Tourism trails could contribute to cross-border integration, vindicating the substantial money spent on such projects in INTERREG programmes. However, border-related barriers remain robust even for tourism projects that are best practices of cross-border cooperation. As such, there is an unfulfilled potential of tourism trails in their contribution to cross-border communication and social cohesion in many European borderlands.