This is a pretty difficult one for me... It's probably Howth, a small seaside village in Dublin, Ireland. I remember visiting it from time to time when I was a kid, so there's a lot of happy memories there. When I eventually moved to Dublin to go to university, I took a girl I was crushing on there for a little day trip. It was such a lovely, sunny day, and we hadn't seen each other for 2 years. We sat overlooking the cliffs just catching up; I don't remember laughing so much in my life.
The combination of blue skies, ocean air, and this amazing girl I hadn't seen in forever really made a real imprint on me.
We still go back there from time to time to just go for a walk, look through the Sunday Market, and generally just enjoy the atmosphere. There's something really charming about little seaside towns.