Have tub, will travel
Try this with a spa pool. We reckon "portable" should actually mean "portable"!
The tub is on the snow groomer heading for the top of the Remarkables skifield near Queenstown, New Zealand.
Near the top of the mountains is Lake Alta, frozen over in winter, a white saucer surrounded by jagged peaks.
And every year a bunch of mad SCUBA divers arrives, chainsaws a hole in the ice, and goes diving. The ice in 2004 was 1.2m (4 ft.) thick and the water in the whole measured 0˚C (32˚F).
We let the tub roll from the top of the rise down on to the lake. Fortunately it stopped just short of the opening!