On one side my first option always has been Oporto airport (OPO) that I know so well and where I'll surely be many more times in the future. It would add a special flavour to each visit.
(it's also called Francisco Sá Carneiro after a portuguese prime minister that died...
when his plane fell after a bomb exploded in flight... Don't ask me how someone decided to give his name to an
airport)
On the other hand I've been many times on Cabo Ruivo, also known as "Doca dos Olivais" (Olivais dock). I participated on a public competition, back in 1994, still as an intern of architecture, when it was decided to renew the place for the then upcoming EXPO 98. We didn't win, but I visited it many times, before, during and after the Exposition.
This is how it was on the time the Seaport was operational
Then it was abandomned and became a depot
And the EXPO turned it in one of the most valued areas in Lisbon.
The building on the center is the Oceanarium, and would make an excelent base, since it's isolated on the water, being acessible just by a bridge.
Also I love seaplanes! I made models as a kid/teenager, and I had this
And this
They make lots of sense in the SSSS universe, because land areas are much more dangerous, as we've seen. So when people return to flying machines seaplanes would be a logical choice, and having a base with a handy dock in calm waters...
So I'll think about it, but I like the idea. If anyone has another suggestion I'd love to hear it
