Kindly suggest the best options for travelling to limpias from lisbon.
Well. It's a long way! If you have a car, that's another matter, but assuming you don't...
Either get to the central bus station in Bilbao (there's a shuttle bus), then get a bus to Laredo (www.alsa.es, there are plenty), and then get a bus to Limpias from Laredo (9 a day - for timetable check here: www.transportedecantabria.es).
Or you can get a FEVE train direct from Bilbao to Limpias (http://www.renfe.com/viajeros/feve/index.html 2 a day), however look on Google maps and you'll see the station is a short walk out of the centre.
Thank you very much for your reply. I'm considering taking a flight lisbon-bilbao and athe train from bilbao to limpias.
However, could you kindly advise the other option lisbon-santander-limpias, which route (lis-bilbao or lis-santander) is quicker and easier?
There is no direct flight from Lisbon to Santander, you would have to fly via Madrid or elsewhere. In terms of getting from Santander to Limpias, the same applies as from Bilbao, you could either get the ALSA bus from Santander to Laredo and then another bus from Laredo to Limpias, or get the FEVE train from Santander to Limpias station. These are the same buses and trains as from Bilbao, just coming from the other direction. (both the FEVE train and the bus lines are Santander-Bilbao).
If you have questions specific to Bilbao, it is best to ask them in the Bilbao forum: http://www.tripadvisor.com/ShowForum-g187454-i517-Bilbao_Vizcaya_Province_Basque_Country.html