Etterstadlottet, also known as Etterstad 1, is a historic landmark in Oslo and represents OBOS' first housing association, established in 1931. The building is characterized by light, high brick walls that surround a large courtyard, and has 103 apartments located around an atrium garden. The stately entrance area with balcony gives the building a distinctive feel reminiscent of a royal castle, even though the concept is aimed at ordinary people.
In 2021, the 90th anniversary of OBOS' housing association building was celebrated, which marks the importance of Etterstadslottet in Norwegian housing history. The building's unique architecture and design have made it a well-known landmark in the area, and it stands as an example of early 20th-century residential construction in Oslo.