Santander is known as one of the most elegant and beautiful cities on the north coast of Spain. In addition to its landscapes and beaches, there are places and plans that make the Cantabrian capital a city with a difference.
Arriving from the airport: Getting to downtown Santander from the airport is reasonably straightforward. There is a bus (S4) which connects the airport to Santander bus and train stations (in the city center). The fare is around 3.00€ per person and you can consult the time-table here. Alternatively, you can take a taxi from immediately outside the airport terminal (this should cost around 25-30€).
Buses: The best option is to use Moovit (https://moovitapp.com), which generally has all the lines,
and up-to-date information or https://transportedecantabria.es/. You can buy a ticket directly from the driver, or on most buses you can pay directly using a credit or debit card with one of the contactless terminals as you get on.
Taxis: There are a number of taxi ranks dotted around Santander, where you can simply jump in the next taxi. You can also request a local taxi to pick you up using the PideTaxi app (https://pidetaxi.es/en/), or calling +34 942 333 333. Another option is Cabify, which is a Spanish version of Uber/Lyft. You can get the app here: https://cabify.com/en/.
Travel to Bilbao Airport: To get to Bilbao airport from Santander, one option is to take a taxi, but this is likely to cost around 180€. In this case, it might be feasible to group together to share a taxi. Alternatively, you can take a coach directly from Santander Bus Station. These coaches should be booked in advance online (https://www.alsa.es) and take ~90 minutes, depending on the specific route, to get to Bilbao Intermodal Bus Station. You can then take bus number A3247 to Bilbao airport from directly within the bus station (https://www.bilbaoturismo.net/BilbaoTurismo/en/del-aeropuerto-a-bilbao). This short journey takes about 20 minutes (and the buses depart every 20 minutes or so).