Hôtel van Eetvelde, Art Nouveau mansion in Squares Quarter, Brussels, Belgium.

Hôtel van Eetvelde is an Art Nouveau town house at 4, avenue Palmerston, built by Victor Horta from 1895 on a plot nine metres wide. Its facade shows an exposed steel frame with slightly projecting floors and windows framed by vertical mullions and gently arched lintels. Inside, an octagonal rotunda with a stained glass cupola carried on eight steel columns serves as a winter garden.

Victor Horta designed the house for Edmond van Eetvelde, secretary-general of the Congo Free State, and it was built from 1895 on a nine-metre-wide plot at 4, avenue Palmerston. Horta added a corner building with a private entrance at no. 2 in 1899, then a four-metre annex at no. 6 in 1901. The gas industry federation bought it in 1950 and converted it to offices; the 1988 restoration rebuilt the rotunda skylight, and further restoration followed in 2022 and 2023.

The house takes its name from Edmond van Eetvelde, secretary-general of the Congo Free State, who commissioned it in 1895 to host receptions. In the corner building at No. 2, the office woodwork in light Congolese mahogany and coral was made to his wishes and survives as one of Horta's finest interiors.

The house stands at 4, avenue Palmerston, with the 1899 corner extension at no. 2 and the 1901 annex at no. 6, near the corner of square Marie-Louise in the Squares Quarter. The entrance door sits at the far end of the main facade rather than in the centre. The building is used as offices, so the interior is not generally open to the public.

The eight-sided roof window above the atrium glows in green, pink, and orange, creating shifting light patterns throughout the day in the rooms below. These colored light rays demonstrate how the architect blended industrial materials with artistic intent.