Bilbao and surroundings - day trips
 

Hello. Next year the whole company I work in will be going to Bilbao for a weekend. I think of extending the stay by a few days and do both some more sightseeing of Bilbao and explore the surroundings. So far I was thinking:

Day trip to San Sebastian.
Organized day trip to sights San Juan de Gaztelugatxe, Bermeo, Mundaka, Gernika-Lumo. I see several offered trips to one or more of these sights?

Are there any other suggestions? One idea could be a hike somewhere in the vicinity or bus/train to a smaller town and renting a bike doing a day tour of 60-80k on a bike from there. Or other towns and sighs worth exploring within an hour or so by train or bus from Bilbao.