I've been to lots of places on Earth, but having considered this question for a while and narrowed them down one by one, the last two have been difficult to separate, but I'm going to say staying at a friends In-laws on the Llyn Peninsular a few miles south of Abersoch on a sailing holiday and on a gloriously warm and clear summers evening looking over the bay to the mountains of Snowdonia in the distance.
Glass like seas, a happy period in my life, I was so content at that time it was perfect sitting there on the bench in the garden taking in the view.
I guess it's not just the scenery, but the state of mind you have at the time as well, and that evening will always live with me.
”Yes, I think I’m going to keep it out!“ replies the other.
P.S. São Paulo is not making this list. Ever. ;-P
Concrete jungle with numerous tent cities in and around the parks. Was warned to leave my watch and wedding ring in the hotel safe and carry a minimum of cash around!