His collapsible bathtub

When, in July 1906, the Tsar unconstitutionally dissolved the Parliament, a number of its members, my father among them, held a rebellious session in Viborg and issued a manifesto that urged the people to resist the government. For this, more than a year and a half later, he was imprisioned. My father spent a restful, if somewhat lonesome, three months in solitary confinement, with his books, his collapsible bathtub, and his copy of J. P. Muller's manual of home gymnastics.

(V. Nabokov, Speak, Memory)