We have a sauna / wellness / fitness room of nearly 40m2 in the basement. It contains a shower, a sauna (3x2.5m), a sling trainer, a rowing machine, a hammock, and a TV. That fills the room quite well.
The advantage of the basement is that even when it’s 35° outside in summer, it’s a comfortable 22° for training inside. The room has a ventilation system and is built out like a living space, including the hallway leading to it, so there’s no "basement atmosphere" on the way there. For the view, there’s the TV. Since I usually train after 9 p.m., it’s dark during the winter months anyway.
On a 3000m2 property, I would also love a fitness room with a view of the garden – but at our place, too many neighbors would be watching me train.
A wellness room with sauna, whirlpool, a view of nature (preferably lake or sea view), and a private terrace with a pool and counter-current system would of course be a dream. But for that, I’d first need a bigger lottery win.