This is admirably simple: In 1876 Ethelbert Watts invented a portmanteau that doubles as a bathtub:
“The object of my invention is to provide a portmanteau, valise, traveling-bag, or other equivalent article used for the transportation of clothing, which shall be convertible into a bath-tub, so as to afford travelers in places where such conveniences are wanting the luxury or comfort of bodily ablution.
“Articles of clothing, &c., may be packed and carried in it as in any portmanteau or equivalent device. When it is desired to use it as a bath-tub the portmanteau is opened, as shown in Fig. 1, and the contents removed. Water is then poured in, when a bath may be enjoyed, as in a permanent tub or fixture. When the bath is over, the water is poured or dipped out, the interior dried by any suitable means, and the device is again ready for use as a portmanteau.”