It is not an actual, physical place. It is wherever (and whenever) I am low in pain, cool enough to be able to think and with all the materials and ability that I need to be able to be creative in the way I need to be at that particular moment in time. That said, there are some places that are much less happy than others, but that usually relates to the people that are there or the situations that happen in those places. So, nebulous wibble aside, my happiest place is, well, … me!
The question I answered here, in case they change it, was, "Where is your happiest place on earth?"