Madrid.

I fly from Heathrow with Iberia to Madrid at 10.30am on 5th December, staying in an AirBnB centrally and then fly back to Heathrow on 8th December at 3pm. Feel free to join at any point and join me for as much or as little time as you want. I am going to explore by foot, see Christmas markets and have nice dinners in the evening. I don't go clubbing but you are welcome to do so.
You will have to sort out your own flight and accommodation.
If there are other people joining up then perhaps you could get an AirBnB together.