Four Days in the Basque Country

In both SS and Bilbao the old towns are easily identified and small.
A drive along the coast will be lovely. Hiking to the flysch formations near Zumaia was a highlight for me.
While in Mundaka, we did a nice walk but I’d love to return one day and do some kayaking in the wetlands.
Check out Elanxtobe, a cute little place where you can walk up for some nice sea views.

Not secrets by any means but, for a daytrip, highly recommend Bar El Gran Sol in Hondaribbia, for the absolute best pinxtos, with a stop at the Chillida Leku open air museum. Both awesome!

My wife and I are about to leave for Spain for two weeks to see some of the Tour de France. That part of the trip is pretty well taken care of, but after, we will be in the Basque Country for four days. We will be staying in Mundaka with a car we will return in Bilbao on the morning of the fourth day and we will fly out of Bilbao for Barcelona the next morning.
We have a few things we want to see and do, but have time for more.

Our plans include (in no particular order) the Guggenheim, Guernica, The beach in Donostia/SanSebastian and the Peine de Viento. We have nothing more as a definite planned "must see/must do".

Any suggestions? A food tour maybe? We did one in Barcelona a few years ago and enjoyed it. If yes, any particular food tours? We like to walk around aimlessly and just see what we see, but a suggestion as to where to go would be great. (For example, El Gotic in Barcelona was well worth getting lost in.) Any similar neighborhoods in Bilbao or Donostia? Any secret little must see or must do places or activities you would recommend?

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You need to have a parking garage in Mundaka, as parking in the street is heavily restricted during the summer season. It´s always scarce, but even more now that it´s for residents only from 3pm every day.

You may want to visit Bermeo (go to the old port, end of the road). Also, probably San Juan de Gaztelugatxe, but most likely you will not be able to do the climb as tickets are now not available (fully booked for most days). In Gernika, you do need to visit the CAsa de Juntas, one of the oldest parliaments in the world, and our Tree of Gernika, so symbolic for us and the expression of our liberties (and one of the reasons John Adams -and John Quincy-) were here in 1780, for 9 days. Ignore the Peace Museum, it´s a bore.

Your best option for lunch (THE main meal of the day, NOT dinner) is the "menú del día" or daily menu, for approximately 20EUR you get a full meal with a bottle of wine for two, in many restaurants in the area. Again, it´s lunch what matters, not dinner, you´re in the Basque Country and it´s something "sacred" for us (and all over Spain).

It´s a very rainy area (although we are now in a very unusual heat wave), almost 200 days of rain per year in Donostia/San Sebastian, so come prepared. Do not expect a beach resort, it´s a city with three beaches, but climate is normally not sunny.

Beautiful and very lively old town in Bilbao, as well as the Hanging Bridge (Puente Bizkaia) outside the city, in Getxo (beautiful seaside town).

Elantxobe, Ea, Lekeitio...but parking is complicated at this time.

(for some reason, English speakers have a problem with the spelling of "pintxos" (and not pinxtos)...do not know why!)