I've always wanted a turret. With a gym on the ground floor, and an orangery extension for plants, a fabulous bathroom on the second floor and an art studio on the top floor. I even know where it would fit on our house. It would look utterly preposterous but I don't care.
Also an underground sauna, dug into the slope.
I would also quite like deer fencing around my entire garden so that my roses would have a chance.
Finally I would like a freeze-drying machine so I could make those wonderful freeze-dried raspberries and also apple slices from my own produce.
I think the £400k (and some) is all gone.