The nearest international airport is the Francisco Sá Carneiro Airport [OPO] in Porto. It is located 11 km northwest from the centre of Porto. The airport is well connected, with numerous public transport options as well as 24/7 taxi services. See official information here
Guimaraes is located approximately 55 km from Porto, train is the easiest, cheapest and most convenient option of getting there.
If you are going directly from Porto Airport to Guimaraes, the most convenient way is to take the Metro Line E (Purple line) to the Campanha train station (the journey is 33 minutes) and a train to Guimaraes leaves from here every hour (the journey is approx.1h 10min). The venues (Centro Cultural Vila Flor and the Hotel De Guimaraes) are a few-minute walk from the train station in Guimaraes.
For more information about the Metro, please click here
For more information about trains, the prices (regular train fare is EUR 3.20 for a single journey), schedules and to book tickets, please click here
If you are arriving a day early and wish to spend some time exploring the city centre of Porto, the most central train station is Sao Bento.