The Circus- und Clownmuseum is a small, unusual Vienna museum devoted to circus history, stage props, costumes, posters, and rotating exhibitions. Its appeal is niche, but it suits Leopoldstadt's old fairground associations around the Prater.
It is best treated as a short specialist stop rather than a headline museum. Pair it with the Prater or Kunst Haus Wien if you want a less formal side of the city.