There’s some terrific waterfront running located ~5 km of the center of Vigo, on the Paseo Marítimo around the Bouzas Port, and then along Samil Beach and several other smaller beaches. A route of up to 13 km, with options for shorter. Beach also runnable!
Starting at Bouzas Port at the Igrexa de San Miguel de Bouzas, the first section is along the Paseo Marítimo, a multi-use path that juts out to the Ria de Vigo (bay), with great water views! It’s 4.6 out and back. Then, continue west along the waterfront promenade path. It’s up to 4 km one-way, passing several small beaches, and then the 1.2 km Samil Beach. Nice water views the whole way. The 1.2 km Samil Beach is also nice for running.