Douro River exploration with red buoy under white Ponte de Sao Joao, and Maria Pia bridge backdrop

porto portugal ponte san joao st johns bridge douro river rabelo red buoy ponte dona maria pia eiffel rail infrastructure iconic architecture river view maritime exploration scenic journey water reflection historic bridge infraestructure slow motion nautical adventure white colored concrete edgar cardoso concrete portico picturesque landscape travel experience bridges nautical traditions engineering marvel six bridges cruise leisure activity waterway passage steel structure tourist attraction boat excursion maritime history under the bridge water transport iconic landmark maritime charm suspended arches river crossing european architecture metalwork riverside leisure travel famous bridge architectural wonder structural elegance cityscape travel memories