Kildrummy sounds tempting!
This one is a little tricky. It would have to be a water I know and I am split between Scotland, Norway and the US.
I think it would have to be a day on Loch Ness with my dad in May, stopping for a shore lunch of bacon rolls cooked on an open fire washed down with Nescafe coffee (the only time it tastes good is when you are fishing). This would be a mixture of traditional loch style and some dry fly fishing from the boat and a bit of trolling when things are slow.
The runners up would again be late May in Norway at my regular fishing spot with my buddy Keith. It is a mixture of lochs and streams. The fish are not big but great fun on my Shay 8' 4wt bamboo fly rod. Again a shore lunch but this time some Norwegian bread, spekkemat and goat's chesse.
3rd place would be up in the Moosehead area of Maine, USA. There are some nice small streams and beaver ponds with brook trout. This one with my 7'6" bamboo and fishing streamer flies or attractor dries. Lunch of moose steak sandwich washed down with a blueberry wheat beer (has to be Seadog).