For me, it would be the Overcliff Hotel in Southbourne, Bournemouth in the summer of 1974. I hadn't started school by this time but it was still my fourth consecutive summer holiday staying there. My older siblings and parents had been holidaying there since at least the mid-1960s. It was to be our last holiday there. I'm not sure what the weather was like but I can clearly remember the green loo under the stairs (it scared me!), the dining room and the bar with the fruit machines and Fox's Glacier Mints. Very fruity but oddly-tasty orange juice that I now swear was laced with Phenergan - never had it since. Student waitresses, one of whom was called Shirley - I decided all of them must be 'Shirleys'. And getting lost in the corridors!
There was also the Fisherman's Walk gardens with its big fish pond and bandstand and the beach of the same name with a zigzag path leading down to it. And the lovely coloured globe lights all along the promenade.
The Overcliff has long since gone. I last saw it standing in 2001; there is now a fancy apartment block called 'Seascape' where it once stood.
I'd go back in the blink of an eye, even if just for an hour or so.