The 70s home that we recently purchased had an outdated built-in display case on the wall that separates my den from the kitchen. (I suspect that maybe there was a window there long ago and that the den was an addition to the house.)
I decided to open up that wall and put a breakfast bar there. That would give us a nice view of the den's fireplace and also allow some light to flow in from the patio door.
As it turns out, there was a header above that display case, so there was no need for me to build a support wall. (For info on how to build a support wall for a passthrough, This Old House has a good video on it).
Once the job was done, it was a huge improvement. The house has a more open feel, and the views are much better!
Here is how I did it step-by-step. I've also included the YouTube video if you'd rather watch that.