Any Japanese bathtub. It's deep, you can fill it to the very top, and it's designed to overflow rather than deprive you of the top 1/3 with an annoying safety drain.
Perhaps tangential, but it still astounds me how Americans scoff whenever I mention that we have floor drains in Australian bathrooms. "What, is your bathroom a locker room or something? snicker". Setting aside how it helps with potential flooding* and makes the floor tiles infinitely easier to clean, it also allows things like this.
*I've also had comments like "why would your bathroom ever flood???" as if nothing water related could ever go wrong.
Astounds me Australians have only one drain. In Finland TWO drains is now preferred. Especially in student dormitories and such. The reason is that people pass out in shower and block the drain.
In cold climate water damage can be fatal, because of heavy insulation and subsequent mildew bloom in it.
I was also surprised that most American showers only have a temperature control and not pressure, and the toilets waste several litres of water every flush.
The good ones are quite tiny and make out of a single piece of fiber, at least that's what they look like. All corners are round and there's a floor drain meaning you can make a splash and not worry about it. Their small size makes them ideal for hotel rooms and apartments alike where space is a premium. Since they are prefab you can also put them into the garden as standalone modules which some people prefer.
