Cornwall is beautiful, still wild and full of picturesque walks. It's famous for its dramatic views, charming fishing villages, abundant plants and mild climate (they even have palm trees!) - which makes it a perfect place for autumn or spring getaway.
I' a big fan of the whole dinner with a view thing (who isn't?) and the west coast of Portugal seems to be perfect for that. Just pick a random spot (that's excatly what we did, no planning ahead) and you're likely to find a restaurant with the freshest seafood and an ocean view.
Douro Valley is at its best off season - I went there last October and would definitely recommend this place for a fall trip. Get ready for postcard-pretty vineyards (famous for they ports, but pretty skilful when it comes to other wines as well), delicious food and picturesque views. Stay in one of the charming vineyards and spend your days on walks in the vines, scenic drives along the river and picnics on the hills.
I'm sure you all know, at the very least more or less, how to make pesto. This is just to remind you that pesto is always a good idea: for a quick pasta dinner, as an addition to a sharing platter, on what to do with herbs from your garden.