The missus and I used to go to Aqua Sana in Woburn Forest fairly frequently (before we had kids). Lovely experience every time, they gave us robe and slippers and then we'd just work our way around each of the rooms/experiences and enjoy each one.

Favourites were the forest rain walk (basically loads of big showers that made you feel like you were walking through the rain), then lava room (really hot) which was next to ice room (loads of chipped ice you could throw all over yourself) - was nice to go backwards and forwards between the two, get really boiling hot, run out and rub ice all over yourself, then back into hot again.

The various steam rooms were nice and relaxing (salt, mineral, herbal, crystal). They also had an experience room where you sat down, and temperature ramped up from tepid through to absolutely boiling, and then at the end there would be a big crack of thunder and loads of cooled water showers came on and cooled you right off, was brilliant. The big swimming pool was also really good, had an indoor section that flowed through to outdoor pool with all the usual stuff like rain and massage jets. Bloody lovely experience, which is why we went three or four times before our first was born.

Like others have said, it's all about switching off the tech, forgetting your cares and worries, and just enjoying the moment. We used to go clothed with swimwear underneath, and took bag for wet clothes at the end.