10 things to do in Bilbao
1. Look at the art outside and the architecture of the Guggenheim museum. (free)
2. Visit a winery. The winery Gorka Izagirre is located 20 minutes by car from Bilbao city centre. They offer at tour of the wine production and wine tasting. They produce wine to a restaurant with several Michelin stars. The wine tasting was very nice and costed 25 euro per person.
https://www.gorkaizagirre.com/en/visits-and-tastings/
If you have more time you can also visit the Rioja district that is about 1,5 hour from the city centre by car.
3. Visit the Guggenheim museum to see the art inside.
4. Visit the food market in Bilbao by the river. (free entrance)
6. Stroll by the river in Bilbao city centre. (free)
7. If the weather is nice, you can visit a beach. You can go to the beach by the metro or by taxi. It takes approximately 30 minutes from the city centre. Bring you own towel. (cheap if you go by Metro)
https://www.bilbaoturismo.net/BilbaoTurismo/en/playas-a-un-metro
9. Walk around and enjoy the paintings on the bridges and doors in the street. (free). This art was in the area of the ground station for the cable train Funicular and across the river over the bridge from the Guggenheim museum.
10. Visit the town San Sebastian by the sea and take a surfing lesson, swim or eat great food. There is a bus from the airport, you can also take a taxi from Bilbao. The train seems to take a very long time.