It's hard to think of a perfect day, just because I'm always thinking of what I need to do, or what else I could be doing, or who else should be with me. But....
Grandma and I went up to a ski resort once in the summer, no skiing, obviously, and it was good rates. We got a sorta-condo at one of the lodges. We went out horseback riding, took the ski lift to the top of the mountain and walked back down, lovely crisp sunny weather the whole time, ate out at a nice local restaurant, used the fireplace that night as it got chilly, and talked and, from a big cushy couch, watched the fire burn down to a perfect bed of coals before retiring to the bed in the loft. In the morning, I made some omelets that came out just right, and we were in robes that came with the room, sitting on barstools at the counter, eating the eggs, sipping at champagne, and looked at each other with the same thought that I voiced: "This is perfect."
So I guess that was a perfect day, because we said so.