santa's workshop

The mythical structure, usually envisioned as located at the North Pole, where Santa Claus and a large number of capable elves work tirelessly and gladly year-round to produce all of the toys and other gifts to be delivered throughout the world on Christmas Day.

A fanciful replica of this structure, temporarily erected in a retail store, shopping mall, or other public venue at Christmastime as an attraction for children and parents.

(idiomatic, by extension) A busy, productive large or small work environment, populated by dedicated workers.