How do you make a nine metre-long long pool infinite? By turning it into a giant Sodastream* of course.
Square footage in central London comes at a premium, and the Savoy's pool — hovering above the ceiling of the theatre — is a pretty but pint-sized affair.
Rather than ping from end to end like a suicidal goldfish though, you're invited to press a button, triggering an almighty jet stream at one end.
All at once it's as if someone's popped in a giant Alka-Seltzer; the pool starts fizzing with a torrent of water, and a strong current is conjured up from the (shallow) depths.
Suddenly you find yourself swimming, yet going absolutely nowhere. The water effectively goes on forever — take THAT nine metres!
The Savoy's pool comes with all the usual hotel extravagances too: bath robes, loungers, sauna and steam room. And if the fizz has put you in the mood, there's a world-leading cocktail bar a couple of flights down.
But the real beauty of this pool is that you can choose whether to have it still or sparkling. Great stuff, as long as you don't find yourself sharing with someone who wants the opposite.
A day pass to the pool, including steam room and sauna is £60
*Other effervescing machines are available