Swimming in an oxygenated or ozone-treated really is a treat compared with the average public pool. The water is less chlorinated, which means your eyes don't get as sore, nor your skin as dry; your hair won't suffer as much either. It also seems to make it easier to swim for longer.

The water in an oxygenated or ozone treated pool really does feel fresher and cleaner than you may have been used to and it's so much easier and more pleasant to swim in that you find you swim a lot longer. There is also the advantage that you don't smell strongly of chlorine when you come out.

After a sauna, Swedes are encouraged to run outside and roll around in the snow. A plunge pool is designed to work on the same principle of really boosting your circulation by going from a heat treatment to a quick cold splash.

Is it a pool, is it a bath? Well, really it depends where it is and how big it is. But as we're the Good Spa Guide, and Jacuzzis in spas tend to be communal, we're classing it as a pool.

A Jacuzzi is a (usually) circular pool/bath, large enough for several people, with a seat-level inside. The water is usually quite hot and bubbles vigorously. Jets of water provide gentle massage and a bubbling water surface for a more invigorating and luxurious bath. An outdoor Jacuzzi is a real treat as you watch the bubbles leak steam into the cold air, while you snuggle down in your hydro-blanket. Think James Bond and champagne.

A whirlpool is similar in many ways to a Jacuzzi, a whirlpool features warm water, underwater jets to massage your body, and constantly moving water.

Salt-water pools are increasingly popular in spas because they help to balance the chlorine in the water and so reduce the stinging eyes you often get in highly chlorinated pools. They are also a more luxurious experience than swimming in a "regular" pool as the water in salt-water pools feels much softer, and leaves your skin feeling soft rather than dried out. It's a similar sensation to swimming in an oxygenated pool, except there may be a kind of salty residue left around the edge of the pool, or on your skin but it's not unpleasant. The swimming sensation is really lovely.

Courtesy of the Good Spa Guide