The campsite we're in is pretty close to a metro line into Porto and the campsite folks called us a taxi to get there, which cost the princely sum of 6EUR. The Porto metro line is very good - clean, modern and pretty fast - and soon deposited us in the centre of town. The main tourist office is nearby so armed with tourist maps we started to work our way down to the river, as that seems to be where a lot of the interest is - plus everyone recommended we take a boat trip on the Douro.
I'm not quite sure what I was expecting from Porto but the reality was much better, as it's a UNESCO world heritage site with lots and lots of historical interest in the town centre. We took a walk along the north side of the river and booked onto one of the boats for a bridges river trip. That gave us a bit of time to walk over one of the main bridges (which has a high and a low level) to check out the port wine warehouse area and see if there was anything related to my namesake "Grahams Port". Turns out there was and we grabbed a photo with a sign before heading back over the river to catch our boat trip.
Walking a little bit further up the river meant we'd managed to get on one of the quieter boats which initially headed up river to go under the various bridges that way. It then turned back down river to go under the final bridge - in fact the one we were ourselves going to drive over the next day.
We then did some more wandering on foot beside the river before heading back to the metro (via a lot of climbing of stairs to get back to the higher level of Porto) and then home. The metro station near the campsite was right beside a big designer outlet place but while we had a walk round be didn't actually spend any money for once!