The Hundertwasserhaus is a unique apartment building located in Vienna, Austria. It was designed by the famous Austrian architect Friedensreich Hundertwasser and completed in 1985. The building features an unconventional and colorful design, with undulating floors, a patchwork of different colors and materials, and a green roof covered in vegetation.

One of the most distinctive features of the Hundertwasserhaus is the absence of straight lines in its design. Hundertwasser believed that straight lines were "godless and immoral," and instead favored irregular shapes and curves. The building also incorporates elements of nature, such as trees growing from the windows and a grass-covered roof, as Hundertwasser believed that nature should be incorporated into urban spaces.

The Hundertwasserhaus has become a popular tourist attraction in Vienna, drawing visitors from around the world to marvel at its unique design. The building also contains shops, restaurants, and cafes on its ground floor, adding to its vibrant and lively atmosphere.