Hi Sea...
I remember your Beach metaphor... it's similar to a homework exercise I had in therapy - to draw pictures of different feelings. I had a full page of logo-type symbols on the "bad" feeling side and only a few on the "good" side - and it didn't even occur to me to try to draw "happy". That's been a long time ago now.
And it just came up the other day, for me, with my brother - a business event was very successfully completed yet he wasn't happy about it, at all. And I had one of those split-second realizations about how different our realities are - yet I USED to be in his reality, all the time. I used to not be able to describe "happy"; didn't know how that feeling actually FELT; didn't believe it EXISTED.
Didn't this thread start out wondering about what it felt like to be excited, looking forward to an event? Versus anxiety, dreading, or just indifference? Aren't they just flip sides (yin/yang) of the same experience? If A exists, then B does too. The yin/yang symbol isn't an either/or, B or W, symbol - it's an "AND" - and the teeny, tiny place in the tails is where negative turns positive in processes and vice versa - yet there always exists the black circle in the white, etc. A&B co-exist continually. If it exists, you can find it; experience it; feel it.
I'm not sure at all about the criteria of a process - the how-to - but I am sure that it is possible to learn new feelings for most people, even if you can't recall feeling that feeling before... like in your beach example. Helen's idea has merit; some people might actually be able to build a completely visualized experience in their imagination, right down to sensory & emotional input... and so be able imagine a new experience and new feelings. But another way would be to go exploring out into the world - a voyage for new experiences, new ways of being - a voyage of discovery... and being open to what comes without superimposing our old experience of "this is what I always feel in THAT situation"... and maybe, when fear is involved, it requires having a trusted "buddy" or "wingman" to go along and back you up... until the fear dissapates and confidence replaces it.
There must be other ways of "how-to", too. I can't really say how I moved from A to B; what I did. I can't pinpoint exactly what changed... or how... or why... if it was something that just magically "happened"... or if I was working on bits & pieces of it all at once and was too zoomed in on those details to notice that change had occurred. All I'm sure of is that it DID happen and I didn't realize it until after the fact. The sunshine is brighter, the rain is fun to play in, gray days are cozier with a book & a cup o' tea and even feelings and boundaries are clearer than they've ever been, as far back as I can remember clearly. (I can almost see them like a matrix or ley lines sometimes)
If you want to badly enough, I'm sure you'll find your own way to this SL - or if not, you'll at least make peace with it.