What a lovely mystery! Now of course the area around Muckross House has plenty of opportunity for taking day trips on horseback through the lovely countryside there, but the main thing we'd want to figure out is where the cottage for lunch was! And if we can't find the exact one, I'm sure that there will be alternatives in the area.
Do you happen to have any photos of the trip that might help identify this day trip?
In the meantime you could have a look at some of the day trips on horseback
in Co. Kerry and in Killarney National Park that are available today, maybe one of them can help jog your memory?