The COVID-19 pandemic has triggered severe global restrictions on international travel with the intention of limiting the spread of SARS-CoV-2 across countries. This paper studies the causal effect of the partial relaxation of these travel restrictions in Europe on the COVID-19 incidence in Germany during the summer months of 2020. It exploits the staggered start of the summer school breaks across German states as an exogenous shock to the travel opportunities of the population. While the school breaks also increased mobility within Germany, the event-study type regressions precisely control for domestic mobility and local COVID-19-related restrictions. The intention-to-treat effects of the relaxed travel restrictions show a significant and sizable increase of the COVID-19 incidence in German counties during the later weeks of the school breaks. Part of the increase can be attributed to a mandatory testing regime for travel returnees from high-incidence areas.