Dom Luís Bridge
PTE Luiz I, 4000 Porto, Portugal
Amazing views of PortoDom Luis bridge in Porto was designed by the man responsible for the Eiffel Tower, and is the subject of many a travel photo. You can walk across it on two levels but I'd recommend taking the top level from Porto to the port wine cellars of Vila Nova de Gaia then staggering back along the lower level. The views from the top are spectacular but you need to keep an eye out for metro trains along the top level.
If you're feeling too lazy to cope with an uphill climb back to your hotel, take the funicular from beside the bridge back up to Batalha.