Strindbergshuset, Karlaplan, Apartment building at Karlaplan, Stockholm, Sweden.

Strindbergshuset, also called Röda huset, was a five-storey Neo-Romanesque building erected 1896–1898 at the corner of Karlaplan, Karlavägen and Narvavägen. Its red patterned brick facades had two round corner towers facing Karlaplan and extra towers on the side wings, plus a tower room with no function or connection to the floor below. The V-shaped plan enclosed a courtyard, and the building was demolished in 1969.

An earlier building on this site was home to Swedish writer August Strindberg from 1901 to 1908. The original structure was demolished in 1969 and replaced with the current construction.

The nickname Strindbergshuset comes from August Strindberg, who lived on the fourth floor of the Karlavägen wing from 1901 to 1908. There he wrote three novels, including Ensam, and about fifteen plays such as Oväder and Ett drömspel. The view from the flat inspired the "growing castle" in Ett drömspel, modelled on the new Hästgardeskasernen.

The building sits centrally at Karlaplan and is easily reached by public transport. The area offers cafes, shops, and other conveniences within walking distance.

The plot's triangular shape came from the meeting of Karlavägen and Narvavägen at Karlaplan. Builder Carl Oscar Lundberg first put up a small two-storey Neo-Gothic brick house in the backyard to meet the deadline requiring a plot to be built on, then built the main house in front of it. The rear building's windows ended up facing only the courtyard walls.